Ventilator

ABSTRACT

A fully pneumatic ventilator capable of both pressure-cycled and volume-cycled operation. A flow controller operates on the basis of a difference between two control pressures, the lesser of which gradually increases during each inspiratory phase of a breathing cycle, to give a flow which starts out at a relatively high rate and is gradually reduced until cut off. In volumecycled operation, the ventilator employs a cycle generator and a time-volume valve to generate an inspiratory time, a ratio between the expiratory time and the inspiratory time, and to set a volume to be delivered. The time-volume valve enables independent setting of the volume and the inspiratory time. The cycle generator and the time-volume valve supply the flow controller with its control signals, and in turn supplies the patient with the breathing gas. There is a relief valve to avoid exerting too much pressure on the patient&#39;&#39;s airways, and there is a vacuum relief preventing too great a suction upon them. An override ends an expiratory phase and starts a new inspiratory phase if the patient seeks to initiate inspiration. In the pressure-controlled mode of operation an airway pressure sensor and controller is employed, and the cycle generator and the time portion of the time-volume valve are not used. Various safety features are provided in both modes.

United States Patent 1 Ollivier Sept. 4, 1973 [52] US. Cl. 128/1453, 137/63 R [51] Int. Cl A6lln 16/00 [58] Field of Search 128/1455, 145.6,

l28/l45.7, 145.8; 137/63 R [56] References Cited UNITED STATES PATENTS 6/1972 Sundblom et al 128/1458 8/1970 Foster 128/l45.6

OTHER PUBLICATIONS Fourth Cranfield Fluidics Conference, Logic Circuit of Artifical Respirators Primary Examiner-Richard A. Gaudet Assistant Examiner-G. F. Dunne Attorney-Owen, Wickersham & Erickson [57] ABSTRACT A fully pneumatic ventilator capable of both pressurecycled and volume-cycled operation. A flow controller operates on the basis of a difference between two control pressures, the lesser of which gradually increases during each inspiratory phase of a breathing cycle, to give a flow which starts out at a relatively high rate and is gradually reduced until cut off. In volume-cycled op eration, the ventilator employs a cycle generator and a time-volume valve to generate an inspiratory time, a ratio between the expiratory time and the inspiratory time, and to set a volume to be delivered. The timevolume valve enables independent setting of the volume and the inspiratory time. The cycle generator and the time-volume valve supply the flow controller with its control signals, and in turn supplies the patient with the breathing gas. There is a relief valve to avoid exerting too much pressure on the patients airways, and there is a vacuum relief preventing too great a suction upon them. An override ends an expiratory phase and starts a new inspiratory phase if the patient seeks to initiate inspiration. In the pressure-controlled mode of operation an airway pressure sensor and controller is employed, and the cycle generator and the time portion of the time-volume valve are not used. Various safety features are provided in both modes.

53 Claims, 14 Drawing Figures RA DRY RATIO PUSH& HOLD l ER 0 INSPI T I12 350 ga es sur e EFFORT INSPIRATORY VOLUME TIME-second milliliter a PRESSUREfl VOLUME 034/. 4 OFF/ 2000 370 CYCLED CYCLED 103 121 .INSPIRATORY PRESSURE SENSITIVITY TIME cm OF w gER cm OF WATER A L5 2 (5 210 9 5 t- 132 I o 4 0 e & g

BREATHS PER VERIFLQ 380/ K 257 we MUTE j PATENIEBSEP 4 ma 31756229 sum 3 0F 8' FIG. 2 79 SUPP!) 5 30%: b

Pc 6 5O 51 3O "r Fc O LON OFF NORMAL OPERATION 30 E PCz 0 i ON OFF ON OFF gIGH F R 30 a E AT ON T O p ON OFF TIME 3 INVENTOR. LOUIS A. OLLIVIER BY UmwMM-$W ATTORNEYS PMENTED SEP 4 I975 SHEEI t Of 8 I I TIME 3 4 TIME CONSTANT TI SETTING 10o- H64 TIMING NETWORK B -4 '3 m T -2 A R E N E G I E 5 L o W m C q n u O 4. 3 2 1 m2; EQEEQXw 053 F INSPiRATORY TIME i Pmmsnm 4m 3756229 SHEEI- 5 0F 8 SUPPLY LPN! AVERAGE INSPIRATORY FLOWRATE i OUTLET FIGS INSPIRAYTORY TIME 5e 1 OOO SOO- PATENTEIISEI 4 ms 3356229 SHEET 6 OF 8 N h 353 CENTIMETER OF MTER 6H s: RATIOITI/TE PUSHIA HOLD INSPIRATORY VOLUME TIME-second miIIiliIer PRESSURE'K VOLUME 4 OFF/ 2000 370 CYCLED CYCLED 9 2 INSPIRATORY PRESSURE SENSITIVITY TIME crn OF WATER cm OFWATER 2o 10- -30 2 go a o 257 MANUAL DELIVERED INSPIRATORY 350 PRESSURE EFFORT IHHII STA RT PATENTEDSEP 4 ms SHEET 8 OF 8 vm wvm mvm mvm

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INVENTOR. LOUIS A. OLLIWER' BY w ATTORNEYS VENTILATOR BACKGROUND OF THE INVENTION This invention relates to an improved ventilator capable of both volume-cycled and pressure-cycled operation.

l-leretofore, the ventilators on the market have been either cycled by pressure or cycled by volume, and they have not been capable of shifting from one form of operation to the other, as is the ventilator of the present invention, where a simple rotation of a selector knob accomplishes the shift. Hence, whereas prior-art ventilators were strictly limited to one of these two types of operation, the present is able to do both. It therefore eliminates the need for an extra machine. Moreover, it is very compact, more compact than any of the volume-cycled ventilators heretofore in use. The present invention enables a single machine to be very versatile and to be adapted to various needs of patients and to the desires of doctors.

A difficulty with ventilators heretofore on the market has been that their flow pattern of delivery has been capable of little, if any, adjustment. Each of them has had a basically fixed flow pattern. It is desirable, from the patients standpoint, to have a large initial flow at the beginning of the inspiratory phase and to have the flow diminish gradually towards asmaller flow at the end of the expiratory phase. The ventilator of the present invention provides a flow pattern which decreases from a maximum value at the beginning of the inspiratory phase to a minimum value at the end of the inspiratory phase. The relationship between maximum and minimum values is maintained independently of the duration of the inspiratory phase and independently of the flow level required to supply the desired volume during the inspiratory phase.

The ventilator of this invention, when used in volume-cycled operation, provides for setting a ratio between the inspiratory time and expiratory time in the breathing cycle. This adjustment, once set, is maintained until purposely reset, but a wide range of such ratios is readily obtainable. Thus, this ratio setting enables full control of the patients breathing cycle, on the basis that the longer it takes to inhale, the longer it takes to exhale and on the basis that, for a given time to inhale, it may be desirable to vary the time to exhale.

In its volume-cycled mode the ventilator of this invention is also capable of a separate noninteracting adjustment of the volume and the inspiratory time, so that either the time or the volume can be changed without significantly changing the other, whereas heretofore adjustment of one would require adjustment of the other each time a change is made. In this invention there is a novel interaction of parts that automatically accommodates these adjustments.

The device senses the patients airway pressure, and the patient can override the normal cycle and initiate a new inspiratory phase in the volume-cycled mode, the effect of the resulting vacuum being used to trigger this action. In the pressure-cycled mode, the patient's airway pressure generally initiates the new inspiratory phase, but there is also a timing device for initiating a new inspiratory cycle if the patient should fail to do so after a predetermined period. Upon initiation of a new inspiratory phase, the ventilator feeds the breathing gas to him at a doctor-set rate and manner. In both modes of operation, the patients safety is assured by a pressure-activated safety relief valve that vents excessive airway pressure to the atmosphere; excessive vacuums are similarly relieved from the atmosphere through a vacuum relief valve.

In normal breathing, from time to time a person will take an exceptionally deep breath and then exhale that deep breath. This sigh may be useful in maintaining or inducing health conditions. Most breathing machines make no provision for other than consistent uniformity. The device of the present invention makes it possible for the doctor manually to cause such a sign whenever he wishes and to continue to induce sighs for as long an intervalas he wishes, each sigh increasing the inspiratory phase in both volume and time by about fifty per cent, while maintaining the ratio between inspiratory time and expiratory time, therefore increasing the duration of the expiratory time also by about 50 percent. This is done without having to change the regular cycling, so that when the doctor releases the sigh actuator, the normal cycle returns.

An inspiratory phase may be initiated at any time during the expiratory phase by pushing a manual start button. The pressure and the vacuum are indicated on a gauge.

SUMMARY OF THE INVENTION In volume-cycled operation the invention controls the inspiratory time, the ratio of the inspiratory time to the expiratory time, the volume, and the sensitivity. A pneumatic cycle generator initiates an inspiratory phase during which a flow controller delivers breathing gas to the patient. The duration of the inspiratory phase is set by an inspiratory time knob on the housing of the device, and the volume of gas delivered during that time is set by a volume knob. The inspiratory phase is followed by the expiratory phase, and the duration of that phase is set as a factor of the inspiratory time by a ratio-adjusting knob. At the end of the expiratory phase, another cycle is automatically initiated. 0verride functions are available, as is a manual sigh. A feature of the operation of the volume-cycled mode is the independence from the impedance presented by the patient in his airway resistance and lung compliance. Since a severe obstruction in the airway might cause the pressure built up by the volume delivered to be very high, the invention takes care of that contingency by providing a pressure relief valve that exhausts part of the volume into the atmosphere if and when a given pressure limit is reached, the pressure limit setting being adjustable. There is also a vacuum release to open the airway connection to atmosphere if the patient draws a vacuum greater than a preset limit.

. In the pressure-cycled mode of operation there are controls for sensitivity, pressure, and flow. In this mode of operation a breathing cycle is initiated as the patient draws a slight vacuum. Initiation locks the command signal in the flow controller, which then delivers breathing gas to the patient. The inspiratory phase is terminated when the pressure created by the patient at the outlet of the ventilator reaches a predetermined pressure setting. The flow of the breathing gas may be adjusted by the volume knob, which works in conjunction with the flow controller. The volume delivered is thus determined by the pressure setting and the flow adjustment, which have an adequate range to cover the cases to be treated. The expiratory phase normally lasts until a new cycle is initiated by the patient as he draws a slight vacuum. However, if the patient has not started a new cycle after a certain time limit, which can be set, the invention provides for an override switch to initiate automatically a new inspiratory phase.

This brief summary gives some indication of what the invention can do, but other objects and advantages of the invention will appear from the following description of a preferred embodiment.

BRIEF DESCRIPTION OF THE DRAWINGS In the drawings:

FIGS. 1A and 18 comprise a pneumatic circuit diagram of a ventilator embodying the principles of the present invention, with some parts shown representationally in elevation and in section. An inset plan view of the gear controls for the time-volume valve assembly shows their actual positions, which cannot be shown correctly in the sectional view.

FIG. 2 is a simplified view in elevation and in section, combined with a functional diagram, of a cycle generator used in the circuit of FIG. 13.

FIG. 3 is a group of graphs showing the functioning of the two signals sent out by the cycle generator under two different types of conditions, normal operation and sigh operation, plotting pressure against time.

FIG. 4 is a graph of the first order timing constant of the timing network, plotting change of pressure against time. I

FIG. 5 is a graph of the ratio of the inspiratory time to expiratory time as a function of inspiratory time, as provided by the cycle generator for three different ratios.

FIG. 6 is a functional diagram and simplified view in elevation and in section of the flow controller employed in the pneumatic circuit of FIG. 18.

FIG. 7 is a graph showing the domain of application of the ventilator in terms of volume delivered versus inspiratory time.

FIG. 8 is a front view of a ventilator housing containing the principal items shown in FIGS. 1A and 1B and providing the various controls.

FIG. 9 is a side view of the ventilator housing of FIG. 8.

FIG. 10 is a fragmentary view in elevation and in section of the time-valve portion of the time-volume valve, enlarged with respect to FIG. 1B and shown more representationally.

FIG. 11 is a view in elevation and in section of the volume-valve portion of the time-volume valve, enlarged with respect to FIG. 18 on the same scale as FIG. 10 and at right angles thereto and shown more representationally.

FIG. 12 is a view in elevation and in section of the main operation switch.

FIG. 13 is a view in elevation and in section of the pressure sensor and controller, enlarged with respect to FIG. 1A and shown more representationally.

DESCRIPTION OF A PREFERRED EMBODIMENT A ventilator embodying the principles of this invention is shown functionally and, to some extent, representationally in FIGS. 1A and 18. Some conventional parts, such as a face mask or other means for connection to a patient are omitted, while other conventional parts are only indicated by words and arrows.

Some normal directions of gas flow are indicated, but

it should be understood that in some conditions there is back flow in some of these conduits. FIGS. 2, 6 and 10-13 show enlarged sectional views, somewhat more representational than FIGS. 1A and 18. FIGS. 8 and 9 show accurate representational views of the exterior of a preferred assembly.

The ventilator of these drawings is capable of both pressure-cycled operation and volume-cycled operation, one at a time. Some parts are used in both modes of operation, while some are used only in one mode. It will be apparent to one skilled in the art to which this invention relates that a volume-cycled ventilator embodying the principles of the operation could be made omitting parts used only in the pressure-cycled mode and omitting the parts employed only in the change over from one mode tothe other. Similarly, a pressurecycled ventilator can be made using the appropriate parts of the device that is shown for the purposes of iilustration. No separate illustration is seen to be needed to support this fact and to support the claims drawn to a single mode of operation.

Referring to FIGS. 1A and 18, a supply 20 sends a desired breathing gas under pressure into a main supply conduit 21. This supply, suitably regulated, may be either pure oxygen or a mixture of oxygen with nitrogen and possibly some other gases. The gas may come, for example, from a ratio-controlling device such as is shown in U. S. Pat. No. 3,534,753, issued Oct. 20, 1970.

Regulation of the Gas Supply (FIG. IA') The main supply conduit 21 may conduct the breathing gas by a branch conduit 22 (FIG. 1A) to a pressure regulator 23, which provides a regulated supply for both the cycle generator 50, the airway pressure sensor and controller 200, and the switch time override 280. The regulator 23 accepts the supply pressure to the ventilator, which may be at from 35 to 50 p.s.i. and reduces it to a constant figure such as 30 p.s.i. A conventional regulator design may be used, having a diaphragm 24 in a housing 25, backed up by a bias spring 26. An inlet 27 is connected to the conduit 22 and leads by suitable passageways into a chamber 28 closed by the diaphragm 24 and having an outlet 30. The force applied by the spring 26 can be adjusted, as by a screw 31. The diaphragm 24 is thus subjected in one direction to the outlet pressure and in the other to the force of the spring 26. The diaphragm assembly may actuate a poppet 32 to admit the flow necessary to maintain a balanced condition. The force of the spring 26 is preset by the screw 31 so that the balanced condition corresponds to a desired outlet pressure, e.g., 30 p.s.i. The regulator 23 may be quite compact and fit easily into a small ventilator housing 380 (FIGS. 8 and 9) along with many other elements.

Main Operation Control Switch 35 (FIG. 1A)

From the outlet 30 of the pressure regulator 23 a conduit 34 leads to a main operation control switch 35, which determines the mode of operation, volume cycled or pressure cycled. The gas is led into an inlet 36 near the periphery of a generally cylindrical but tapered housing or body 37. The switch 35 has two positions, one for the volume-cycled mode (as shown in solid lines) and the other for the pressure-cycled mode (as shown in broken lines). The basic functional part of the switch 35 may be a tapered Teflon plug 38 which rotates in the tapered body 37. In the volume-cycled mode, a flat surface 39 machined on the surface of the plug 38 provides the desired interconnection from the port 36 to a port 40 by the resulting clearance from the body 37. A second flat face 41 and a radial passageway 42 provide a connection between a port 43 in the body 37 and an axially extending passageway 44 in the plug 38, having two outlets 45 and 46. There are also ports 47 and 48 in the body 37. 1

When the switch 35 is in its volume-cycled mode position, the regulated supply from the conduit 34 is led by the switch 35 from the port 36 to the port 40 and into a conduit 49 which conducts it to a cycle generator 50, (FIG. 1B).

The Cycle Generator 50 (FIGS. 18 and 2) The cycle generator 50 is shown, in simplified form, in FIG. 2. It has a housing 51, preferably made up of several individual pieces, and it has a series of dia' phragms 52 and 53 in one portion and 54 and 55 in another portion. The regulated supply conduit 49 leads in through a port 56 to a central axial passageway 57. The diaphragms 52 and 53, which are of different area, are carried on the same diaphragm plug 58, and at one end of the plug 58 is mounted a closure seat 60.

A chamber 61 bounded at one end by the diaphragm 52 is provided at its other end with a wall 62 that seats a spring 63 hearing against a shoulder 64 of the diaphragm plug 58. A chamber 65 lying between the two diaphragms 52 and 53 is open to the atmosphere through a port 66, and another chamber 67 is bounded at one end by the diaphragm 53.

In the chamber 67, an adjustable spring seat 68 is provided for a spring 69, which bears against the lower end of the plug 58. The adjustable seat 68 is threaded to a stem 70 which leads outside the housing 51, and on it a gear 71 is mounted. The gear 71 is meshed with a larger gear 72 in a magnifying-gear train, for control by a handle 73 on a shaft 74 carrying the gear 72. As will be seen later, this handle 73 sets the ratio of the inspiratory time to the expiratory time when the ventilator is in its volume-cycled mode.

The chamber 61 is in communication with another chamber 75 by means of conduits 76, 77, and 78, and the conduit 78 is also connected by a conduit 79 to a restricted bleed 80, which bleeds off to atmosphere at a controlled rate.

The chamber 75 in th housing 51 is closed at one end by the diaphragm 54. A chamber 81 lies between the diaphragms 54 and 55 and a chamber 82 lies outside the diaphragm 55. Both of the diaphragms 54 and 55 are carried on a plug 83, which also carries a valve seat 84 adjacent a valve port 85 leading from the chamber 82. The chamber 82 is vented to atmosphere by another port 86.

From the chamber 75 a passageway 86 leads to a side passage 88 that is normally closed by a spring 89 biasing a valve 90 to the closed position. When the valve 90 is open, the passage 88 is connected to a chamber 91 having a port 92 that is connected to a conduit 93.

A port 94 from the chamber 67 is connected by conduits 95 and 96 to a port 97 leading into the chamber 81 so that the chambers 67 and 81 are kept at the same pressure, and the conduit 95 is connected to a conduit 98 that is connected to a conduit 99. The conduit 98 is also connected by a time valve 100, (shown basically as a needle valve in FIG. 2 but soon to be explained in more detail with reference to FIG. IE) to a conduit 101, which is connected to the conduit 93 and also to a conduit 102 that is connected to the port 43 of the operation switch 35. The conduit 101 is also connected to the port 85, so that the ports 85 and 92 are connected together.

Operation of the Cycle Generator 50 From a functional standpoint, the cycle generator 50 uses a supply regulated at, for example, 30 p.s.i. to generate two signals, designated as PCl at the conduit 102 and PC2 at the conduit 99 and to vary their relative values as a function of time within a given cycle and also to repeat the cycle continuously. Each cycle has two phases, an ON-phase corresponding to the inspiratory phase of the ventilator and an OFF-phase corresponding to the expiratory phase of the ventilator.

During the ON-phase (see FIG. 3, top line) the signal PCl is at a constant pressure, e.g.,. 30 p.s.i., while PC2 (next line below in FIG. 3) increases from a minimum preset pressure, which may lie between 1 and 6 p.s.i., to a maximum preset pressure, which may lie between 17 and 22 p.s.i., for example. These preset pressures can be varied as desired, each over a range of values, but, once set, they remain constant during a given operation.

During the OFF-phase, the signal PCl is bled to atmospheric pressure through the port 86, and is therefore zero above atmospheric, while the signal PC2 decreases from its preset maximum value to its preset minimum value. The span between the minimum and I the maximum values of the signal PC2 is constant, but the levels of the values vary within a band of approximately 5 p.s.i. This variation establishes the ratio between the ON-time and the OFF-time in a given cycle. Under the limit conditions just mentioned, for example, the ratio goes from about 1:3 to about 1:1.5.

The two signals PC] and PC2 are sent, as will be described later, to the flow controller 140 to establish a flow of breathing gas. The flow from the flow controller 140 is proportional to the difference (PCl PC2). During the ON-phase there is flow, and this flow starts at a maximum value at the beginning of the phase and decreases as PC2 increases, reaching its minimum value at the end of the ON-phase. The flow is shut off during the OFF-phase because PCl becomes zero, and the difference (PC1 PC2) is therefore negative.

Let the effective areas of the two diaphragms 52 and 53 be A1 and A2, and the forces created by the springs 63 and 69 be F1 and F2. The diaphragm assembly and the plug 58 assume two different positions, in one position (open), the seat 60 is away from the inlet 57 which is connected to the regulated pressure of gas in the conduit 49, and in the other position. (closed) the seat 60 is against the inlet port 57 and shuts off the flow that would otherwise come through it.

In the open position the supply pressure transmitted through the inlet port 57 becomes PCl, which is applied to the smaller area diaphragm 52 and is also sent via conduits 76, 78, 77, chamber 75, passages 87, 88, chamber 91 and conduit 93 to the conduit 101, the port 85 being closed. A flow is established from PCl through the needle valve to build up the pressure PC2 in the conduit 98 and against the larger area diaphragm 53.

In the closed position the inlet port 57 is closed by the seat 60. The pressure PCl bleeds out from the chamber 61 to atmosphere through the conduits 76, 78

and 79 and the fixed bleed hole 80; the port 85 is opened to bleed off the conduit 101 immediately, and the pressure PC2 more gradually decreases as it flows in the reverse direction back through the needle valve 100 to the conduit 101 and thence to the port 85 and to atmosphere through the bleed port 86.

The two conditions in which the diaphragm assembly 52, 53, 58 switches from one position to the other are determined by two balances of forces:

1. The diaphragm assembly opens the inlet port 57 when F1 (PC2 min. X A2) F2.

2. The diaphragm assembly closes the inlet port 57 when F1 +(PC1 X A1) (PC2 max. X A2) F2.

The two conditions of balance are unstable. In condition (1), as soon as the inlet port 57 opens, a force (PCl X Al) is added to F1 to keep the seat 60 away from the port 57. This condition prevails until the condition (2) is reached, and when it is reached, the inlet port 57 closes and PC] bleeds off to atmosphere, so that the force opposing (PC2 X A2) F2 is suddenly decreased by the amount (PCl X Al). This keeps the diagragm assembly and its seat 60 against the inlet port 57 until the next condition (1) is reached. Thus, the system cycles continuously between the two conditions.

Combining the two equations (1) and (2) we can obtain 3. PCI X A1 APC2 X A2, or

APCZ PCl X Al/A2.

The minimum value of PC2 is determined by F1 F2. In this instance F1 is a fixed force, while F2 is adjustable. The maximum value of PC2 is [PC2 min. APCZ].

The duration of the ON-phase is the time that it takes PC2 to go from its minimum value to its maximum value, and the duration of the OFF-phase is the time that it takes PC2 to go from its maximum value to its minimum value. Although the change in PC2 is the same in both phases, the corresponding times are not equal, due to the fundamental characteristic of a pneumatic timing circuit. This is shown in the curve of FIG. 4, which shows the time it takes for a step change in pressure to be transmitted into a capacity through a needle valve. The time it takes to reach 63.2 percent of the total step is called the time constant of the circuit. Since this case concerns a resistance R and a capacity C, it is known as a first order or RC network circuit, and the time constant is a first order time constant. The curve is plotted as percent recovery versus time expressed in terms of the time constant.

For example, assume that APC2 is 16 p.s.i. and consider that in one case PC2 goes from 1 to 17 p.s.i. and in a second case PC2 goes from 6 to 22 p.s.i.

In the first case, in the ON-phase the total step being 30 p.s.i., since PCl changes suddenly from to 30 p.s.i., the pressure PC2 goes from l/30 3.3 percent of the step to 17/30 56.5 percent .of the step. In the OFF-phase, the total step being 17 p.s.i. as PC1 changes suddenly to 0, the pressure PC2 goes from 0/17 0 percent of the step to 16/17 94 percent of the step. In terms of time, the ON-phase is [0.82 0.05] 0.77 time constant. Similarly, the OFF-phase is 2.85 time constant. The ratio of ON to OFF is therefore 0.77 to 2.85 or 1 to 3.7.

In the second case, in the ON-phase the total step being 30 p.s.i. again, the pressure PC2 goes from 6/30 20 percent of the step to 22/30 73.5 percent of the step. In the OFF-phase, the total step being 22 p.s.i., PC2 goes from 6122 which equals 0 percent of the step to 16/22 73 percent of the step. In terms of time, the ON-phase is [1.30 0.25] 1.05 time constant. Similarly, the OFF-phase is 1.30 time constant. Hence the ratio of ON to OFF is 1.05 to 1.30 or about 1 to 1.2.

An inspiratory time knob 103 is connected to the needle valve 100, which sets the time of the ON-phase. This will be discussed later in connection with the timevolume valve 110. The valve 100, though incorporated in a separate volume-time valve assembly 1 10 is associated functionally with the cycle generator 50. The ratio knob 73 is connected to a mechanical drive which changes the value of the force F2 by changing the compression of the spring 69.

Within the practical range of ratios from 1 to 1.5 to 1 to 3, the actual inspiratory time stays within 10 percent of a given setting (by the knob 103) as the ratio is varied (by the knob 73) within its range. This fact is illustrated by the graph shown in FIG. 5, which is made from data obtained with a typical unit.

The additional circuitry incorporated in the cycle generator 50 has the purpose of assisting a rapid switchover from the ON-phase to the OFF-phase and thus to increase the accuracy of timing. This accuracy is especially important at fast cycling rates, where they may be, for example, above 50 per minute. The pressure PC! is applied to the inlet of the timing needle valve 100 through the check valve 90. The diaphragm assembly 54, 55, 83 works in cooperation with the port 85 to bleed to atmosphere the pressure PCl upstream of the timing valve 100 at the start of the OFF-phase. This happens in the following sequence: During the ON-phase PCl, which is greater than PC2, keeps the seat 84 against the port 85. At the end of the ON-phase the pressure PCI upstream of the check valve bleeds off to atmosphere through the fixed bleed 80. During that very short time the check valve 90 maintains ICl upstream of the timing valve 100, thus keeping PC2 at its maximum value. Once the pressure PC] upstream of the check valve is lower than the pressure PC2, the diaphragm assembly 53, 54, 83 moves the seat 84 away from the port 85, and the pressure PCl downstream of the check valve 90 is rapidly bled to atmosphere through the chamber 82 and the port 86. The OFF-phase proceeds, as PC2 decreases by flowing back through the timing valve to atmosphere via the ports 85 and 86.

The cycle generator 50 may be assembled in a stacked type of force-balance construction. The diaphragms 52, 53, 54, and 55 may be made from a high strength Fairprene, an elastomer coated elastic fabric, conservatively stressed during operation. The two diaphragm assemblies are the only moving parts. The motion is substantially friction free, and the travel is small, about l/32 inch to l/l6 inch. The variable compression spring 69 is actuated by the gear-driven screw 70, the gear train 72, 71 magnifying the action of the ratio knob 73 and providing a more precise and more stable setting through a 270 full scale rotation to cover a selected ratio range, such as from 121.5 to 1:3.

The Time-Volume Assembly (FIG. 1B)

A time-volume valve assembly 110 incorporates the needle valve 100 associated with the cycle generator 50 to set the inspiratory time and a valve associated with the flow controller to set the volume. It also includes mechanical drives to actuate the two valves 100 and 120. This assembly 110 features a unique compen sation network through which the volume valve 120 receives two inputs, one from a volume knob 121 and the other from the inspiratory time knob 103, the purpose being to correct the actual opening of the volume valve 120 whenever the inspiratory time is changed, so that the volume delivered continues to be the same as that indicated by the volume knob 12].

The time-volume valve 110 has a housing 111. For the time valve 100, an inlet passage 104 (connected to the conduit 101 through a check valve 109) leads into a chamber 105. The gas entering the chamber 105 at PC1 leaves at PC2 by the conduit 98 after passing through a port 106 in accordance with regulation by a novel stem 107, which is provided with a logarithmic shape and is backed up by a spring 108.

The setting of the opening between the stem 107 and the port 106 is determined by the setting of a screw 1 12 that moves back and forth a forward stem 113 engaging a forward portion 1 14 of the main stem 107. This screw 112 is provided with a spring 115 to assure its seating and is controlled by the rotary position of its shaft 116, on which a gear 117 is rigidly fixed. The time-control knob 103 is secured to a shaft 118 to which is secured a gear 119 that meshes with the gear 117.

The valve 120 is generally similar in construction, with some differences. It has an inlet 122 connected to the unregulated supply conduit 21 and leading into a chamber 123 that provides a valve seat 124. On the other side of the valve seat 124 a chamber 125 is connected to an outlet passage 126 leading into a conduit 127. A plug 130 having a logarithmic exterior surface and backed up by a spring 128 has a stem 129 and is urged into position by a stern 131 in contact with the stem 129. The stem 131 is controlled by a screw 132 that has a back-up spring 133 and a stem 134 supporting a gear 135 that meshes with the gear 119. By means of the gears 119 and 135, the position of the plug 130 is controlled by the time knob 103. However, another gear 136 threaded to the screw 132 is meshed with a pinion gear 137 that is mounted on a shaft 138 having the volume control handle or knob 121.

Thus, the time-valve 100 is a precision valve in which the stem 107 is shaped to provide a logarithmic calibration of the knob 103. This characteristic is extremely desirable for precise setting of the time because it gives an equal percentage calibration. A given incremental rotationof the inspiratory time knob 103 represents the same percentage of the indicated time at any point of the scale. For example, percent of a full scale increment corresponds to 0.05 seconds at a reading of 0.5 seconds, and at a reading of 2 seconds it corresponds to 0.2 seconds. On a linear scale, 10 percent increment on a full scale of 0.4 to 4 seconds means 0.36 seconds at any point of the scale or 20 percent of 2 seconds and 80 percent of 0.5 seconds. The logarithmic characteristic is put to good use in the compensation network. The gear train 119, 117 which drives the needle valve 107 preferably magnifies the action of the time knob 103 and enables a precise setting through a 270 full scale rotation in the range of 0.4 to 4 seconds.

The logarithmically calibrated plug 130 for the volume valve 120 has similar advantages. Equal percentage calibration appliesin the same way to the volume setting. Hence, for example, on a full scale of 200 to 2,000 cc, 10 percent of the full scale increment means 50 cc at 500 cc, cc at 1,000 cc on a logarithmic scale or 180 cc at 500 cc and 180 cc at 1,000 cc on a linear scale. The volume valve 120 is driven either through the gear train 119, 135 or the gear train 137, 136, both of them preferably magnifying the action of the knob 103 or 121 and enabling the precise setting through a 270 full scale rotation in the range of about 200 to about 2,000 cc.

It is desirable that the inlet 104 offer no resistance to the inflow during the inspiratory phase; but for the backflow it is advantageous to provide a resistance in addition to that set by the stern 107 and to make that resistance effective only in the range of the higher flows corresponding to short expiratory times. This is accomplished by the use of the check valve 109 in the inlet 104 and a restriction 139 in parallel with the check valve between the inlet 104 and the conduit 101. During the inspiratory phase, the check valve 109 opens at once and the pressure PCl is applied directly to the inlet 104 from the conduit 101. During the expiratory phase, the check valve 109 is closed and the bleeding of PC2 is governed in part by the restriction 139. The restriction is sized to be smaller than the orifice around the stem 107 during short inspiratory times and larger than that orifice during long inspiratory'times, so that it lengthens the expiratory phase only during expiratory phases that follow relatively short inspiratory times, such as 0.5 to 1.0 second. As a result, the ratio of inspiratory time to expiratory time is maintained more evenly in that time range as well as over the whole time range, as shown in FIG. 5.

The Compensation Network of the Time-Volume Valve Assembly 1110 A very important feature of the time-volume valve assembly is its compensation network. The volume valve actually sets a flow, and the setting for a flow can be expressed in terms of volume for a given time over which the flow is integrated to obtain the volume. For example, if one assumes a time of 1.5 seconds, one can calibrate the valve for that value of time for a volume at 1,000 cc. If the time alone is changed to 0.75 seconds, the actual volume delivered will be 500 cc, since the same flow is integrated over half the time. In

order to correct the opening of the volume valve 120 volume flow X time or using logarithmic values log V logf+ log 1.

Thus, in order to keep log V constant as log t is changed, the change in log f must be equal and opposite to the change in log t.

Since both the time valve 100 and the volume valve 120 are characterized to have a logarithmic indicating scale, their respective indications are proportional to log t and log V. FIG. 1B shows that the volume valve 120 is actuated in two ways; the volume knob 121 drives the gear 137 and that drives the gear 136 in which the screw 132 of the valve 120 is threaded; as the stern 131 is prevented from turning, the rotation of the gear 136 moves the stem 131 longitudinally. On the other hand, the gear 136 may be stationary for a given position of the volume knob 120 but rotation of the threaded stem 134 within the gear moves the stem 131 longitudinally, again changing the opening of the valve 130, 124. This second mode of actuation is connected to the mechanical drive of the time valve 100.

Thus, in an example where the volume is set at 1,000 cc and the time at 1.5 seconds, when the time is changed to 0.75 seconds, the stem 134 of the volume valve 120 is simultaneously rotated within the stationary screw 132 and moves longitudinally to increase the opening for greater flow. The increment of flow change is equal to the increment of time change on a logarithmic basis. Since the time is reduced to one-half of its original value, the flow is increased to twice its original value and as a result, the volume indicated by the knob 121 is preserved. Hence, turning the inspiratory time knob 103 affects the time but does not affect the total volume.

The compensation is effective within the domain of practical application of the ventilator. The limits of the domain correspond to average flows of 12 to 90 liters per minute. Reference may be made to the graph of FIG. 7. Limit examples would be:

at 12 liters per minute, V= 200 and t= 1 second, or

V 600 and t 3 seconds;

at 90 liters per minute, V 750 and t 0.5 second to V= 1500 and t= 1 second.

The Flow Controller 140 (FIGS. 1B and 6) The flow controller 140 is a very important part of this invention. As shown in FIG. 6, it has a housing 141 with three diaphragms, 142, 143, and 144; the diaphragms 142 and 144 have areas A3 that are equal, while the center diaphragm 143 has an area A4 that is smaller. The three diaphragms 142, 143, and 144 are joined by a common diaphragm plug 145. Outside the diaphragm 142 is a chamber 146. Between the diaphragms 142 and 143 is a chamber 147. Between the diaphragms 143 and 144 is a chamber 148, and outside the diaphragm 144 is a chamber 149. Spring pressure is exerted against the diaphragm plug 145 by a spring 150 which is mounted on a movable spring seating member 151, which itself bears on the end of a threaded member 152. The threaded member 152 extends through the housing 141 and, once adjusted, is preferably locked in place by a lock nut 162. A blind nut 153 is then threaded on the member 152 and sealed against a gasket ring 163. For readjustment, the blind nut 153 is first removed and the lock nut 162 backed away. The opposite end of the diaphragm plug 145 carries a seat 154, which is adapted to seat against or to be moved away from a valve opening 155, which is part of the outlet conduit.

Each of the chambers 146, 147, 148, 149 has an inlet. Thus, the chamber 146 has an inlet 156 which is connected to the outlet of the volume valve 120 by the conduit 127. The chamber 147 has an inlet 157 connected to the pressure PC2 by the conduit 99. The chamber 148 has an inlet 158 connected to the pressure PCl by a conduit 161, which is connected to the conduit 102 through the switch 35. Finally, the chamher 149 has an inlet 159 connected to the supply conduit 21. The pressure of the supply conduit 21 may, for the purpose herein be designated P1 and that of the conduit 127 (which is the result of the pressure P1 12 passing through the volume valve may be designated P2.

The flow controller receives two command signals, PC1 and PC2, from the cycle generator 50 and the time valve 100, and it establishes a flow of breathing gas from the valve 154, to an airway conduit 160 proportional to the difference between the two signals, i.e., proportional to (PC1-PC2). The flow is also proportional to the opening of the vvalve 120.

The principle of operation is to generate across the valve 120 a differential pressure proportional to the difference between the two command signals. As indicated previously, the difference (PC1 PC2) is positive during the inspiratory phase and then creates a flow proportional to its value. The flow is at a maximum at the start of the phase and decreases with time to a lower value at the end of the phase. The pattern of flow decreases from maximum to minimum value is essentially the same for all durations of the phase within the range of the inspiratory time for which the setup is designed, typically 0.4 to 4.0 seconds. Since the flow is governed by the difi'erential pressure, which is proportional to (PC1 PC2) and to the opening of the valve 120, a predetermined flow can be set by the valve opening. This flow, integrated over the inspiratory time, becomes the volume delivered by the ventilator during the inspiratory phase. The point should be emphasized that the valve 120 sets a flow. The valve setting can be indicated as a volume setting only for one value of inspiratory time. Remembering the timevolume valve assembly 110, it will be seen, however, that the flow knob 12] can be used as a volume knob independently of the inspiratory time.

During the expiratory phase the difference (PC1 PC2) becomes negative and in this instance operates to shut off the flow controller 140. The functional diagram, FIG. 6, shows how the flow controller 140 generates the differential pressure. The diaphragm assembly is subjected to the forces supplied by four pressures on their corresponding effective areas:

1. Supply pressure P1 upstream of the valve on the area A3. 2. Pressure P2 downstream of the valve on the area 3. The command pressure PC1 on the area [A3 31 4. The command pressure PC2 on the area [A3 The combined forces position the diaphragm assembly to establish a flow which creates the balanced condition defined by:

(P1 X A3) (P2 X A3) =PC1 X [A3 A4] PCZ X [A3-A4].

Thus 1P1 P2] X A3 [PC1 PC2] X [A3 A4].

[P1 P2] is a differential pressure AP across the valve; so

Thus, the differential pressure AP is proportional to [PC1 PC2]. It is positive during the inspiratory phase and is 0 during the expiratory phase when [PC1 PC2] becomes negative, so that the flow controller 140 is shut off.

The outlet port 155 of this valve is adjustable and is used to equalize the effective areas of the diaphragms, and the bias spring 150 is used to adjust the balance for a no-flow condition, so that when [PCl PC21= there is no flow.

THE SIGI-I DEVICE (FIG. 1B)

Sigh and switch override functions may be combined in one functional package, a unit 170 having a housing 171 which is convenient since the two functions have a common connection with the cycle generator.

A sigh is obtained by connecting the additional capacity of a chamber 172 to the PC2 side of the cycle generator 50, via a conduit 173 connected to the conduit 98 and an inlet 174 in the housing 171. When a sigh is desirable, this chamber 172 is used to increase the inspiratory time by a fixed amount, which may be, for example, about 50 percent of a normal time. (See FIG. 3). The additional capacity of the chamber 172 is connected into the circuit by pushing manually on a button 175, which opens a check valve 176 located between the chamber 172 and the inlet 174. When the button 175 is released, a spring 177 closes the valve 176 and a spring 178 urges the button 175 outwardly, and the chamber 172 and its capacity are again isolated from the cycle generator circuit. During the expiratory phase, whether or not the button 175 is held in, the pressure remaining in the chamber 172 bleeds through the check valve 176 until it is equal to the minimum valve of PC2. Then the check valve 176 prevents any increase in pressure within the capacity until the button 175 is pushed again.

When the manual sigh is applied, the increase of the inspiratory time by about 50 percent in turn increases the time by which the flow is integrated, and therefore the volume is increased by about 50 percent. As previously indicated, the ratio ti/te remains unchanged, so that the expiratory time is also increased by the same approximate 50 percent. This is illustrated in FIG. 3, low two graphs.

The switch override portion of the unit 170 comprises a pneumatic switch 180 actuated by a signal that comes from the airway pressure sensor 200, which is explained below, via a conduit 181. When a vacuum condition in the patients airways is sensed by the airway pressure sensor 200, it creates a signal SUflICIBIlt to move a diaphragm 182, and a plug 183 of the override switch, carrying a seat 184 away from a port 185, and then the PC2 pressure from the conduit 98 is bled to atmosphere via the port 185 and a port 186, and as a result, a new inspiratory phase is started when the PC2 pressure reaches its minimum value. The plug 183 is biased toward its closed position by a spring 187, and the signal from the conduit 181 is applied via a port 188 to a chamber 189 between the diaphragm 182 and a second diaphragm 190 carried by the same plug 183 in a single diaphragm assembly.

The pressure PCl is applied from the conduit 101 by a branch conduit 19] and a port 192 to a chamber 193 closed by the diaphragm 190. Thus, the pressure PC] is applied to one end of the diaphragm assembly 182, 183, 190, and the pressure PC2 is applied at the other end of the same diaphragm assembly, while the signal from the conduit 181 is applied between the diaphragms 182 and 190.

During the expiratory phase, the pressure PC1 is zero; so it does not interfere with the initiation of a new inspiratory phase by the override switch 180. At the start of such an inspiratory phase, the pressure PCl immediately is applied to the chamber 193 at its maximum value, and the diaphragm assembly 182, 183, 190 moves the seat 184 against the port 185 and stops any bleeding of the pressure PC2 to atmosphere, assuring that the set inspiratory time will be preserved, since the pressure PC2 begins increasing from its minimum value where it switches the cycle generator 50 to the inspiratory phase and continues to increase at it normal rate.

As breathing gas is delivered to the patients airway, the pressure becomes positive, and the signal from the sensor 200 returns to a low value at approximately atmospheric pressure and the override switch closes its port 185. At the next inspiratory phase, when the pressure PCl returns to zero, the seat 184 remains against the port 185, since the signal from the sensor 200 is very low. The diaphragm assembly 182, 183, 190 and its bias spring 187 are sized to open the seat 184 away from the port 185 when the signal from the pressure sensor 200 via the conduit 181 is greater than about 15 p.s.i. Other values may be chosen if that is desired.

The Airway Pressure Sensor and Controller The airway pressure sensor and controller 200 senses the airway pressure and generates the pneumatic signal that is sent to the override switch 180 by the conduit 181 when the airway pressure is negative and is lower than a value set by a sensitivity knob 210. As has just been explained, this pneumatic signal is applied to the override switch 180 to initiate an inspiratory phase when the ventilator is set to operate in the volumecycled mode. In the pressure-cycled mode the operation is different, as will be seen after the structure has been described.

' and the end of the stem 208 bears on the flat spring 206 and adjusts the force it exerts against the diaphragm support member 205. The stem 208 is controlled by the sensitivity know 210. The chamber 204 has a port 211, connected by a branch conduit to the airway conduit 160, at the outlet pressure from the flow controller 140. Thus, the airway pressure is applied to one side of the large diaphragm 202, while the other side is at atmospheric pressure; as the airway pressure decreases below atmospheric pressure, movement of the large diaphragm 202 is opposed by the flat spring 206.

In communication with the chamber 203, which is kept at atmospheric pressure by a port 212, is a smaller diaphragm 213, supported by a member 214. The support member 214 is also secured to another diaphragm 215, to provide a two-diaphragm assembly. Between the diaphragms 213 and 215 is a chamber 216 having a port 217. The other side of the diaphragm 215 is open to the atmosphere. A spring 218 biases the diaphragm assembly 213, 214, 215.

Below the large diaphragm 202 as seen in FIGS. 1A and 14, is a detector 220. This includes a smaller diaphragm 221 that closes the chamber 204 and defines one end of another chamber 222 which is kept at atmospheric pressure by a port 223. The member 205 also carries a seat 224 in the chamber 222. Many of these ports may be located in the manifold plate 199 in an opening 225 therein. Below the plate 199 is a detector housing 226 in which is a diaphragm 227 that closes the other end of the chamber 222. On the opposite side of the diaphragm 227 is a chamber 228 in the housing 226 that is supplied with gas from the conduit 34 through an inlet 234 and a fixed restriction 229.

The diaphragm 227 is carried by a plug 230 having an extended tubular member 231 and a passage 232 extends through the tubular member 231, the plug 230 and the diaphragm 227 connecting the chamber 228 to the chamber 222, so that, normally, the incoming pressure from the conduit 34 through the restricted orifice 229 flows through the passage 232 and is vented to atmosphere by the port 223. However, when the airway pressure decreases below atmospheric pressure, the reduced pressure in the conduits 160 and 165 acts in the chamber 204 and acts to move the large diaphragm 202 and with it the seat 224 toward the end of the tubular member 231 first throttling the passage 232 and then closing it, so that the pressure in the chamber 228 rises. A spring 233 acts on the sensor diaphragm assembly 227, 230, 231 to provide a positive feedback snap action described later.

The detector 220 incorporates a relay 235 which functions as a power amplifier that provides the actual pressure to the conduit 181. While its output pressure is approximately equal to that of the pneumatic signal furnished by the detector proper, the flow handling capacity of the relay 235 is greatly increased over that of the detector proper. The combination of the detector 220 and the relay 235 gives a fast response; on the one hand, the detector 220 has a fast reaction since its internal volume is very small; on the other hand the relay 235 has a high flow handling capacity to supply the functional assemblies connected to its output.

The relay 235 may be in the detector housing 226 and includes a pair of diaphragms 236 and 237. The upper diaphragm 236 closes a chamber 238, which is connected by a conduit 239 to the chamber 228. The chamber 238 is therefore at the same pressure as the chamber 228, so that that side of the diaphragm 236 is acted on by that pressure, which may here be termed the signal pressure. A chamber 240 between the diaphragms 236 and 237 is open to the atmosphere by a port 241. A chamber 242 below the diaphragm 237 has an outlet 253 connected to the conduit 181. Both of the diaphragms 236 and 237 are mounted on the same support member 243, which has an axial conduit 245 leading to a radial conduit 244 in the chamber 240. The chamber 242 has a lower portion 246 having an inlet 247 connected to the conduit 34 and a poppet valve 248 biased by a spring 249 and acting on a seat 250. An extension 251 of the poppet valve 248 can engage the axial passageway 245 and close it. The diaphragm assembly 236, 237, 243 actuates the poppet 248 so that a regulated pressure equal to the command signal is created in the upper part of the chamber 242. Any difference between the pressure in the chamber 242 and that in the chamber 238 moves the poppet 248 to restore a balance. If the regulated pressure in the chamber 242 is lower than the command signal in the chamber 238, the poppet 248 is opened to let in more pressure from the portion 246 and conduit 34. 1f the regulated pressure in the chamber 242 is higher than the command signal in the chamber 238, the poppet 248 is closed, and the excess in the chamber 242 is bled to atmosphere through the passages 245 and 244, the chamber 240 and the port 241. The spring 249 is retained by a threaded cap 252, which also seals the chamber 246 with the aid of a washer 254.

It will be apparent from this that the sensitivity knob 210, causing the screw 208 to act on the flat spring 206 determines the vacuum at which the large diaphragm 202 and its seat member 224 are able to close off the passage 232, thereby controlling the sensitivity of the device to vacuum conditions in the patients airway. This signal then produces the flow into the conduit 181 from the relay 235.

The housing 201 also may contain a manually adjustable pressure regulator having a stem 256 with a handle 257 acting through a spring 258 on a diaphragm 260 that bounds a chamber 261. The diaphragm 260 carries a support 262 having a stem 263 that can engage a stem 264 on a poppet 265 to move the poppet 265 away from a seat 266, to which the poppet 265 is normally urged by a spring 267. An inlet port 268 is connected by a conduit 270 to the port 47 in the operation control switch 235. An outlet port 271 is connected to a conduit 272, which leads to a fixed bleed 273 to atmosphere and to a conduit 274. The conduit 274 leads to the port 217.

The fixed bleed 273 downstream of the pressure regulator 255 establishes a desirable minimum flow for good response. The bleed 273 is also used in conjunction with the time override valve 280 in determining the initial level of pressure setting when the time override valve 280 is actuated.

When the ventilator is in the pressure-cycled mode,

the pneumatic signal generated at and around the detector diaphragm 227 and transmitted to the relay 235 is sent by the conduit 181 and port 48 through the operation switch 35 to different conduits to perform two different functions. It is applied (1) to the flow controller through the port 46 and the conduit 161 to act as PC1 to produce a flow of breathing gas in the airway conduit 160, (2) at the same time via the port 47, conduit 270, pressure regulator 255, and conduits 272 and 274 to the port 217 and chamber 216 to act on the small diaphragm assembly 213, 214, 215, and (3) at the same time via the port 45 to a pressure switch 320, an exhalation switch 300, and a time override valve 280.

This small diaphragm assembly 213, 214, 215 actuated by (2) above then locks the pressure sensor 200 by positive feedback action on the diaphragm 202 in a position to maintain the pneumatic signal in the conduits 181 and 161 at its maximum value, which is approximately or nominally 30 p.s.i.,--i.e., PCl. However, the full pressure of the pneumatic signal from the conduit 181 is not applied to the small diaphragm assembly 213, 214, 215 for it is reduced by the network which includes the adjustable pressure regulator 255 and the fixed bleed 273 downstream from the pressure regulator 255. The reduced downstream pressure in the conduit 274 creates the force acting on the small diaphragm assembly 213, 214, 215 which is applied to the large diaphragm 202. As the breathing gas is delivered by the flow controller 140, the pressure in the airway conduit increases. When the force on the large diaphragm 202 that is created by the pressure in the conduits 160 and 165 becomes equal to that applied by the reduced pneumatic signal at the port 217, the large diaphragm assembly 202, 205 moves away from the end of the sensor tube 231, and the pneumatic signal in the conduit 181 is bled to its minimum value, i.e., atmospheric pressure. At the same time the pressure acting on the small diaphragm assembly 213, 214, 215 is also bled to atmosphere by the conduit 274 and the bleed 273. Thus, the pneumatic signal in the conduits 181, 161 is kept at its minimum value, and the flow controller 140 is shut off during the expiratory phase.

As noted earlier the adjustable flat spring 206 opposes the motion of the diaphragm 202 towards the sensor tube 231, and a vacuum is required to bring the diaphragm assembly 202, 205 against the sensor tube 231, the amount of vacuum required being adjustable by the sensitivity stem 208. Preferably, the range of adjustment is to 6 centimeters of water.

A positive feedback feature is incorporated in the de tector 220 by having the exhaust nozzle 232 mounted on the detectors diaphragm 227. As the large diaphragm assembly 202, 205 approaches the tube 231, the pneumatic signal in the conduit 181 starts to increase, and as it reaches about half of its maximum value, it overcomes the force of the spring 233 and creates a snap action that holds the nozzle 231, 232 firmly against tthe seat 224, thereby locking the pneumatic signal in the conduit 181 at its maximum value acting through the relay 235. This snap action also moves the seat 224 and the large diaphragm assembly 202, 205 upwardly, the length of the snap-action stroke being limited, in order to prevent excessive movement, by engagement of the plug 230 with a shoulder 275, the distance of movement of the plug 230 being carefully calculated to afford the desired limit. Thus the nozzle 231 and the seat 224 are locked together at this time. Conversely, the pneumatic signal in the conduit 181 starts to decrease from its maximum value when the airway pressure in the conduit 160 is sufficient to move the large diaphragm assembly 202, 205 away from the nozzle end 231. When the signal goes below about one-half of its maximum value, the diaphragm 227 is moved by the spring 233, and the nozzle tube 231 is suddenly moved further away from the seat 224, and the pneumatic signal in the conduit 181 then drops to its minimum value, again by snap action.

As noted above, the large diaphragm assembly 202, 205 is also subjected to the force applied to it by the small diaphragm assembly 213, 214, 215 in a direction that opposes the action of the airway pressure on the large diaphragm 202. This gives a reference force acting in a direction that reinforces the locking action described in the preceding paragraph and provides the force that eventually will have to be undone or overcome by the airway pressure in order to release the lock. There is snap action in both directions. The reduced pneumatic signal from the conduit 274 creates its force on the effective area of the small diaphragm assembly 213, 214, 215, the effective area being the difference between the areas of two diaphragms 213, and 215, and that is the force exerted on the large diaphragm assembly 202, 205. When the reduced signal from the conduit 274 is at its minimum value, the small diaphragm assembly 213, 214, 215 is kept away from the large diaphragm assembly 202, 205 by the light bias spring 218. The reduced signal operating level may be adjustable from approximately 3 to 7 p.s.i., which corresponds to an airway pressure of about 0 to 40 centimeters of water on the large diaphragm. The knob 257 actuating the pressure regulator 255 enables the doctor to set the pressure for this pressure-cycled operation.

Thus, the patient normally initiates a new inspiratory phase, and the pressure-cycled mode, by breathing in and lowering the pressure in the conduits 160 and 165 and in the chamber 204. When the seat 224 closely approaches the nozzle 232, they are forced against each other and moved upwardly by the snap action discussed and the downward movement of the small diaphragm assembly follows. The inspiratory phase, thus started, causes the pressure in the conduits 160 and 165 to increase until the seat 224 is moved away from the nozzle, again by snap action. The expiratory phase, thus started, continues until the next inspiratory phase is initiated. I

Time-Override Valve 280 (FIG. 1B)

A time override valve 280 is also provided in this invention principally for use in the pressure-cycled mode. It is set to receive two inputs, one being the continuous regulated supply from the conduit 34, via a branch conduit 281, the other being the intermittent pressure from the operation switch and the conduits 282 and 283, this being the same pressure PCll as that sent by the conduit 161 to the flow controller 140 at 30 p.s.i. during the inspiratory phase only of the volume-cycled or pressure-cycled modes; this pressure is zero during the expiratory phase. The intermittent pressure from the conduit 283 is supplied through a check valve 284 to a chamber 285 on one side of a diaphragm 286, while the supply pressure from the conduit 281 is applied through a port 287 to a chamber 288 on the other side of the diaphragm 286. The diaphragm 286 may be mounted on a plug 290. A bias spring 291 exerts a force in a direction to move the diaphragm 286 and its seat 292 against an outlet port 293.

When the two inputs are both at about 30 p.s.i., the seat 292 on the diaphragm plug 290 is forced against a seat on an outlet port 293 by the spring 291. When the intermittent pressure drops to 0 during the expiratory phase, a 30 p.s.i. pressure is trapped by the check valve 284 in the chamber 285, and bears against the diaphragm 286. A needle bleed valve 294 bleeds the chamber 285 to atmosphere through a port 295, and when the pressure decreases to approximately 15 p.s.i., the force of the supply pressure on the diaphragm 286 is sufficient to overcome the bias spring 291 and move the seat 292 away from the port 293. The 30 p.s.i. pressure is then applied through the port 293 via a conduit 296 to the chamber 216 of the small diaphragm assembly 213, 214, 215. This in turn acts on the sensor 200 and starts a new inspiratory phase.

The bleed valve 294 is preferably adjusted so that it takes approximately ten seconds from the end of the inspiratory phase to the start of a new one. Of course,

under normal conditions an inspiratory phase would have been started sooner, either (in the volume-cycled mode) by the cycle generator or (in the pressurecycled mode) by the patient, but this is a safety feature to insure that the phase does not run any longer than the time which is set by this time override valve 280.

As noted earlier, the fixed bleed 273, to which the time override valve 280 is connected by the conduits 296 and 274, is used in determining the initial level of pressure setting when the time override valve 280 is actuated.

The Exhalation Switch 200 An exhalation switch 300 is provided to receive a command signal from the outlet 45 of the operational switch 35 via the conduits 282 and 301 and 302, this being the same signal as that which is sent to the flow controller 140 by the conduit 161. In the exhalation switch 300 two diaphragms 303 and 304 are joined by a plug 305, and the signal moves the diaphragm assembly 303, 304, 305 to close a seat 306 against a port 307 or to open it, so that a conduit 308 leading to the port 307 is vented to atmosphere via a port 309. The conduit 308 is connected to the airway pressure conduit 160 through a restriction 310 and is connected through a conduit 31 l to a fitting 312 for a low-pressure exhalation valve. During the inspiratory phase the command signal in the conduits 282, 301, and 302 is at 30 p.s.i.; it then overcomes a bias spring 313 to move the seat 306 against the port 307 and to seal the control line 308 for the exhalation valve fitting 312. During the expiratory phase, the command signal in the conduits 282, 301, and 302 is at atmospheric pressure, and the bias spring 313 moves the diaphragm assembly 303, 304, 305 and the seat 306 away from the port 307 and opens the control line 308 of the exhalation valve fitting 312 to atmosphere. Since the command signal is the outlet of the operation switch 35, the exhalation switch 300 is actuated in both modes of operation, volume cycled and pressure cycled; in the volume-cycled mode a signal from the cycle generator synchronizes the exhalation valve with the flow controller to assure that the exhalation valve will be open during the expiratory phase and closed during the inspiratory phase; in the pressure-cycled mode the synchronizing signal is derived from the detector.

This exhalation switch 300 may be used with a low pressure bladder type of exhalation valve, such as a Bennett valve, for which control pressure is taken from the airway pressure 160 through the restriction 310.

The Pressure Switch 320 A pressure switch 320 is also provided to supply a small nebulizer (not shown but connected to a fitting 321) and a humidifier (also not shown but connected to the fitting 322) with gas, preferably taken downstream from the volume valve 120 and coming from the conduit 127 via a conduit 323 and to do this only during the inspiratory phase. Taking the gas from the conduit 127 means that the portion of the total volume delivered to the patient by the ventilator through the nebulizer fitting 321 and the humidifier fitting 322 is included in the volume set by the knob 121 of the volume valve 120.

The pressure switch 320 receives a command signal from the outlet 45 of the operational switch 35, via the conduits 282, 301, and 324, this being the same signal as that sent to the flow controller 140 via the conduit 161. This signal is applied to one side of a twodiaphragm assembly comprising diaphragms 325 and 326 and a support 327. The signal from the conduit 324 is applied to a chamber 328 on one side of the diaphragm 325, and the gas supply from the conduit 323 is applied to a chamber 329 on the opposite side of the diaphragm 326, via a'chamber 330 that is opened and closed by a poppet 331 and seat 332. The general assembly is like that of the relay 235 and the action is basically similar, though there are some differences.

A chamber 333 between the diaphragms 325 and 326 is vented to the atmosphere through a port 334, and the chamber 329 is vented to the chamber 333 by an axial passage 335 and a radial passage 336 in the support member 327 when an extension 337 of the poppet 331 opens the passage 335. A bias spring 338 acts on the poppet 331.

The diaphragm assembly 325, 326, 327 actuates the poppet 331, so that a regulated pressure equal to the command signal from the conduit 324 is created in the chamber 329. Any difference in pressure between the chambers 328 and 329 acts on the diaphragm assembly 325, 326, 327 and it, in turn, moves the poppet 331 to restore a balance. If the regulated pressure of the signal in the chamber 329 is lower than the command signal in the chamber 328, the poppet 331 is opened to enable flow from the chamber 330 into the chamber 329, whence it flows by an outlet 340 and a conduit 341 to the nebulizer fitting 321 and the humidifier fitting 322. If the pressure in the chamber 329 is higher than the command signal in the chamber 328, the poppet 331 is closed and the excess pressure in the chamber 329 is bled to atmosphere through the passages 335 and 336, the chamber 333, and the port 334.

The pressure in the conduit 341 transmitted to the nebulizer fitting 321 and humidified fitting 322 is about 30 p.s.i. during the inspiratory phase and is zero during the expiratory phase.

A feature of the pressure switch 320 is that it bleeds the connection to the nebulizer very rapidly after the end of the inspiratory phase. This is important in preserving a precise ratio of the inspiratory time to the expiratory time, especially when the signal is also used to actuate a Bird type of exhalation valve as can be done. This type of valve (not shown, but connected to a fitting 342), is operated at high pressure, and when that type of exhalation valve is used, the signal to the conduit 341 is used also for actuating the exhalation valve, through the fitting 342. Only one type of exhalation valve is used at a time; so valves 343 and 344 may be provided to shut off the one not in use.

Since the command signal in the conduits 282, 301, and 324 comes from the outlet 45 of the operations switch 35, the pressure switch 320 is active during the inspiratory phase in both modes of operation, volume cycled and pressure cycled.

The Manual Start 345 In both modes of operation, the physician may desire or require a manual device for initiating a new inspiratory phase whenever he so desires. A manual start 345, shown in FIG. 1A, may therefore be placed in parallel with the switch time override 280, as by a conduit 346 connected to the conduit 272. The conduit 346 leads from an outlet 347 from the manual start 345 to the chamber 216 of the small diaphragm assembly 213, 214, 215. The outlet 347 is connected by a passage 348 to a chamber 349. The passage 348 is normally blocked by a valve seat 365 having an O-ring seal 366. The seat 365 is held in its closed position by a biasing spring 367 but can be manually opened by pushing on a stem 368. The chamber 349 is connected by a conduit 369 to the conduit 34 from the regulator 23. Thus, whenever the stem 368 is pushed, the regulated pressure in the conduit 34 is applied, with some reduction by the bleed 273, to the chamber 216 and an inspiratory phase is initiated. Once so initiated, the phase continues, though the stem 368 is released, until the delivered pressure reaches the value set by the pressure setting knob 257.

Relief of Pressure and Vacuum As mentioned earlier, if the pressure in the airways gets too high, it must be vented, and for this purpose a relief valve 350 is connected to the airway conduit 160. The pressure in the conduit 160 is applied to one side of an O-ring sealed valve member 351 and develops a force which is opposed by the force of a spring 352. The force of the spring 352 can be adjusted by a handle 353 and screw 354, having a return spring 355. When the force from the pressure in the airway conduit 160 becomes greater than that of the spring 352, the valve member 351 is moved and a portion of the flow controller output is exhausted to atmosphere through a valve opening 356.

The pressure at which the relief flow starts may be adjusted by adjusting the compression of the spring 352, which is preferably kept within a range of to 80 centimeters of water. The pressure setting incorporates a locking feature to prevent that setting from being disturbed. This comprises the collar 357 threaded on to the handle 353 and hearing when locked on the support member 358. The pressure limit is a critical factor for the safety of the patient, for if it is too low, it will limit the flow. delivered to the patient and if it is too high, it may permit an excessive pressure to build up in the airway. Hence, it is important that the pressure setting, once determined, be maintained.

As stated earlier, for similar reasons it is important to have a vacuum release, and so a vacuum release valve 360 is connected to the airway conduit 160. The airway pressure is applied to an O-rin'g-sealed valve member 361. When the pressure is positive, the valve 361, is pushed against its seat 362, and when the pressure is negative, there is a force in the direction that tends to move the valve 361 away from its seat 362 and to enable outside air from the atmosphere to flow into the airway conduit 160, so that the patient will at least get air at atmospheric pressure. In order to open the valve 361, the negative pressure has to overcome the force of a bias spring 363, which is set so that the valve will open with a desired pressure, such as 6 to 8 centimeters of water of vacuum.

. Other Connections to the Airway Conduit 160 Also connected to the airway conduit is an outlet group, which may include three outlet connections: (1) a large-diameter, 22 mm. for example, outlet valve 370, (2) the small-diameter outlet fitting 312 for control of an exhalation valve such as the Bennet type, (3) the other small diameter outlet fitting 321 supplied by the output of the pressure switch 320 and connected to a small nebulizer, and (4) the fitting 342 for the Bird type of exhalation valve.

The small diameter connection 312 for control of the Bennett type of exhalation valve is supplied through the restriction 310, which may, for example be l/32 inch diameter. Downstream of the restriction 310 the line is also connected to the exhalation switch 300. When the switch 300 is closed, airway pressure builds up in the control line 308 during the inspiratory phase. When the switch 300 is open, the control line 308 is bled off to atmosphere, and the exhalation valve opens under the action of the airway pressure during the expiratory phase.

The large diameter fitting 370 for the outlet hose incorporates the one-way valve or check valve 371 to prevent back flow of various liquids from the patient during the expiratory phase. This may be accomplished by a thin diaphragm 372 which seals against a perforated body of a fitting on reverse flow but offers little resistance to flow from the ventilator to the airway.

The pressure in the line to the airway may be indicatedby a gauge 375. For example, the gauge may have a diaphragm type pressure sensor driving a pointer in front of a circular dial 376. Preferably, the dial 376 displays two color coded zones, a positive pressure zone 377 from 0 to centimeters of water designated as delivered pressure and a negative pressure zone 378 from 0 to 20 centimeters of water designated as inspiratory effort.

FIGS. 8 and 9 show a commercial embodiment of the ventilator having a housing 380 inside which is the circuit of FIGS. 1A and 18 except for the main supply and the outlet fittings. All the regulatory knobs appear here.

THE OPERATION SWITCH 35 IN USE A summary of what the operation switch 35 does may be helpful. As noted before, the switch 35 has two positions and controls by its change from one position to another all that is needed to change from the volumecycled mode to the pressure-cycled mode and vice versa.

In the volume-cycled mode, the port 36 is connected to the port 40, so that the conduit 34 from the regulator 23 is connected to the conduit 49 that leads to the inlet 56 of the cycle generator 50. Also, the port 43 is connected to the outlet 46 through the axial passage 44, so that the conduit 102 for PCl pressure is connected to the conduit 161 that leads to the port 158 of the flow controller 140. The outlet 45 is, of course, also thereby connected to the port 43 through the axial passage 44, so that the pressure PCl from the conduit 102 is also applied via the conduits 282, 283, 301, 302 and 324 to the time-override valve 280, the exhalation switch 300, and the pressure switch 320.

In the pressure-cycled mode, the port 36 is cut off from the port 40, and the port 43 is cut off from the outlets 45 and 46. In this mode the pneumatic signal from the pressure sensor 200 is connected by the conduit 181 to the port 48 and from there (1 by the outlet 46 to the conduit 16] leading to the flow controller and (2) by the outlet 45 to the time-override valve 280, the exhalation switch 300, and the pressure switch 320. Also, the port 48 is connected to the port 47, so that the conduit 181 is also connected by the conduit 270 to the pressure regulator 255 and from there to the conduit 274, the fixed bleed 273, and the chamber 216.

To those skilled in the art to which this invention relates, many changes in construction and widely differing embodiments and applications of the invention will suggest themselves without departing from the spirit and scope of the invention. The disclosures and the description herein are purely illustrative and are not intended to be in any sense limiting.

I claim:

1. A volume-cycled fully pneumatically operated pneumatic ventilator for connection to a supply of breathing gas, including in combination:

pneumatically operated flow control means for providing breathing gas during the inspiratory phase of 

1. A volume-cycled fully pneumatically operated pneumatic ventilator for connection to a supply of breathing gas, including in combination: pneumatically operated flow control means for providing breathing gas during the inspiratory phase of each breathing cycle at a rate dependent upon the difference between first and second control pneumatic pressures, PC1 and PC2, pneumatically operated ratio control means for generating said pressure PC1 at a constant value and only during the inspiratory phase, for delivering said pressure PC1 to said flow control means, and for determining the ratio of inspiratory time to expiratory time for each said cycle, pneumatically operated time control means connected to said ratio control means for determining an inspiratory time for each breathing cycle, independently of the volume to be delivered, and for generating said second control pneumatic pressure PC2 from said pressure PC1 at a value always less than said pressure PC1 when the pressure PC1 is present, and sending said pressure PC2 to said flow control means, said time control means increasing second control pressure PC2 during the inspiratory phase from a minimum value to a maximum value, then decreasing it during the expiratory phase from said maximum value to said minimum value, and pneumatically operated volume control means connected to said time control means and to said flow control means for determining, independently of time, the volume of breathing gas delivered in each inspiratory phase.
 2. The ventilator of claim 1 having a patient airway conduit connected to said flow control means for providing said breathing gas to a patient, an exhalation valve in said patient airway conduit, and control means for actuating said exhalation valve in synchronization with said time control means, for opening said exhalation valve during each said expiratory phase and closing it during each said inspiratory phase.
 3. The ventilator of claim 1 wherein said time control means is connected to said ratio control means for receiving said pressure PC1 by a parallel network of a check valve and a restriction, means for opening said check valve during each inspiratory phase for rapid flow of gas at said PC1 pressure and for closing it during each expiratory phase, so that said PC2 pressure flows back only through said restriction, said restriction being sized to be effective at the shorter values of the time setting, said ventilator also having means comprising a part of said ratio control means for bleeding said pressure PC1 to atmosphere at the beginning of each expiratory phase.
 4. The ventilator of claim 1 having a manually actuated sigh valve connected to said time control means by a conduit into which said PC2 pressure is delivered, and a sigh chamber to which gas from said conduit is admitted when said manually actuated sigh valve is opened, thereby increasing the capacity of the timing system and lengthening both the inspiratory and expiratory phases proportionately, with proportional increase in volume, while said manually actuated valve is held open.
 5. The ventilator of claim 1 having pneumatically operated override means for actuation by a patient able to initiate a new inspiratory phase before completion of a controlled expiratory phase, comprising a patient airway conduit connected to said flow control means, means connected to said patient airway conduit for sensing a patient-induced vacuum of given value, signal supply means for producing a pressure signal when said given value is sensed, and means for venting said PC2 pressure from its then pressure to its minimum pressure upon application of said signal thereto.
 6. A volume-cycled fully pneumatically operated pneumatic ventilator, including in combination: supply means for supplying a breathing gas at a first regulated pressure P1, pneumatically operated regulator means connected to said supply means and having an outlet for said gas at a second, lower, pressure P2, pneumatically operated flow control means connected to said supply means for providing breathing gas at a rate dependent upon the difference between first and second control pneumatic pressures, PC1 and PC2, a patient airway conduit connected to said flow control means for flow therethrough of said breathing gas, said conduit having an exhalation valve, pneumatically operated ratio control means connected to said regulator means for generating from said pressure P2, the pressure PC1 at a constant value, for delivering said pressure PC1 to said flow control means, and for determining the ratio of inspiratory time to expiratory time for each said cycle, pneumatically operated time control means connected to said ratio control means for determining an inspiratory time for each breathing cycle, independently of the volume to be delivered, and for generating said second control pneumatic pressure PC2 from said pressure PC1 and sending it to said flow control means, means in said ratio control means for causing said first control pressure PC1 to be present only during the inspiratory phase and to be constant during that phase, said second control pressure PC2 being always less than PC1 during the inspiratory phase and increasing continually during that phase from a minimum value to a maximum value, means in said ratio control means for decreasing continually said pressure PC2 during the expiratory phase from said maximum value to said minimum value, pneumatically operated volume control means connected to said time control means and to said supply means at pressure P1 and to said flow control means at a pressure P3 for determining, independently of time, the volume of breathing gas to be delivered in each inspiratory phase, and pneumatically operated exhalation valve control means connected to said time control means and said exhalation valve for synchronizing the opening of the exhalation valve with said expiratory phase and the closing thereof with said inspiratory phase.
 7. A volume-cycled pneumatic ventIlator, including in combination: supply means for supplying a breathing gas at a first regulated pressure P1, regulator means connected to said supply means and having an outlet for said gas at a second, lower, pressure P2, flow control means connected to said supply means for providing breathing gas at a rate dependent upon the difference between first and second control pneumatic pressures, PC1 and PC2, a patient airway conduit connected to said flow control means for flow therethrough of said breathing gas, said conduit having an exhalation valve, ratio control means connected to said regulator means for generating from said pressure P2, the pressure PC1 at a constant value, for delivering said pressure PC1 to said flow control means, and for determining the ratio of inspiratory time to expiratory time for each said cycle, time control means connected to said ratio control means for determining an inspiratory time for each breathing cycle, independently of the volme to be delivered, and for generating said second control pneumatic pressure PC2 from said pressure PC1 and sending it to said flow control means, means in said ratio control means for causing said first control pressure PC1 to be present only during the inspiratory phase and to be constant during that phase, said second control pressure PC2 being always less than PC1 during the inspiratory phase and increasing continually during that phase from a minimum value to a maximum value, means in said ratio control means for decreasing continually said pressure PC2 during the expiratoy phase from said maximum value to said minimum value, volume control means connected to said time control means and to said supply means at pressure P1 and to said flow control means at a pressure P3 for determining, independently of time, the volume of breathing gas to be delivered in each inspiratory phase, and exhalation valve control means connected to said time control means and said exhalation valve for synchronizing the opening of the exhalation valve with said expiratory phase and the closing thereof with said inspiratory phase, said flow control means comprising a diaphragm assembly of three diaphragms, namely, first and second outer diaphragms of equal effective area and a central diaphragm of smaller effective area, a seat at one end of said diaphragm assembly, a first chamber at one end of said diaphragm assembly closed by said first outer diaphragm and having an outlet orifice toward and away from which said seat moves, flow through said outlet orifice being varied according to the position of said seat, said first chamber having an inlet connected to said volume control means at said pressure P3, a second chamber between said first outer diaphragm and said central diaphragm connected to said time control means at pressure PC2, a third chamber between said central diaphragm and said second outer diaphragm connected to said ratio control means at pressure PC1, and a fourth chamber at the opposite end of said diaphragm assembly from said first chamber and connected to said supply pressure P1, compression spring means in said fourth chamber bearing on said diaphragm assembly, and means for setting the degree of compression of said compression spring means, whereby as said pressure PC2 increases during the inspiratory phase and said pressure P1 remains constant, the outflow from said orifice decreases during said inspiratory phase from a maximum to a minimum, and whereby the outflow is shut off during said expiratory phase, as said pressure PC1 is then atmospheric and PC2 is greater than PC1.
 8. The ventilator of claim 6 having pneumatically operated override means for actuation by a patient able to initiate a new inspiratory phase before completion of a controlled expiratory phase, comprising pneumatically operated means connected to said patient airway conduit for sensing A patient-induced vacuum of given value, pneumatically operated signal supply means for producing a pressure signal when said given value is sensed, and pneumatically operated means for venting said PC2 pressure from its then pressure to its minimum pressure upon application of said signal thereto.
 9. A volume-cycled pneumatic ventilator including in combination: supply means for supplying a breathing gas at a first regulated pressure P1, regulator means connected to said supply means and having an outlet for said gas at a second, lower, pressure P2, flow control means connected to said supply means for providing breathing gas at a rate dependent upon the difference between first and second control pneumatic pressures, PC1 and PC2, a patient airway conduit connected to said flow control means for flow therethrough of said breathing gas, said conduit having an exhalation valve, ratio control means connected to said regulator means for generating from said pressure P2, the pressure PC1 at a constant value, for delivering said pressure PC1 to said flow control means, and for determining the ratio of inspiratory time to expiratory time for each said cycle, time control means connected to said ratio control means for determining an inspiratory time for each breathing cycle, independently of the volume to be delivered, and for generating said second control pneumatic pressure PC2 from said pressure PC1 and sending it to said flow control means, means in said ratio control means for causing said first control pressure PC1 to be present only during the inspiratory phase and to be constant during that phase, said second control pressure PC2 being always less than PC1 during the inspiratory phase and increasing continually during that phase from a minimum value to a maximum value, means in said ratio control means for decreasing continually said pressure PC2 during the expiratory phase from said maximum value to said minimum value, volume control means connected to said time control means and to said supply means at pressure P1 and to said flow control means at a pressure P3 for determining, independently of time, the volume of breathing gas to be delivered in each inspiratory phase, exhalation valve control means connected to said time control means and said exhalation valve for synchronizing the opening of the exhalation valve with said expiratory phase and the closing thereof with said inspiratory phase, override means for actuation by a patient able to initiate a new inspiratory phase before completion of a controlled expiratory phase, comprising means connected to said patient airway conduit for sensing a patient-induced vacuum of given value, signal supply means for producing a pressure signal when said given value is sensed, and means for venting said PC2 pressure from its then pressure to its minimum pressure upon application of said signal thereto, said means for sensing comprising a first diaphragm assembly in a housing and having a first large-area diaphragm and a second small-area diaphragm, with a first chamber between them connected to said airway conduit, the other side of said first large-area diaphragm being vented to the atmosphere, the other side of said second small-area diaphragm being open to a second chamber vented to the atmosphere, and a seat supported by said first diaphragm assembly, spring means in said first chamber, and sensitivity control means for setting the pressure exerted by said spring means against said first diaphragm assembly, and a detector assembly having a second diaphragm assembly open at one end to said second chamber and having a tubular extension that provides an axial conduit and is opened and closed by said seat, spring means acting on said second diaphragm assembly to urge it to open said axial conduit, and a third chamber on the opposite end of said second diaphragm asembly, means for limiting tHe motion of said second diaphragm assembly to a fixed amount, and passage means through said second diaphragm assembly into said third chamber from said axial conduit, said third chamber having an inlet with a restricted orifice leading into said third chamber and connected to said regulator at the pressure P2, and a port connecting said third chamber to said signal supply means.
 10. The ventilator of claim 9 having a relay for said detector assembly comprising a third diaphragm assembly having a pair of diaphragms of equal effective areas defining a fourth chamber on one side of said third diaphragm assembly, connected to the third chamber for maintaining the same pressure as in said third chamber, a fifth chamber between said diaphragms and vented to atmosphere, and a sixth chamber on the other side of said third diaphragm assembly, said third diaphragm assembly having an axial opening and a passageway opening from said sixth chamber into said fifth chamber, a seventh chamber joined to said sixth chamber by a port, a poppet for opening and closing said port and having an extension for engaging said axial opening and closing it when engaged by said third diaphragm assembly, said third diaphragm assembly operating when in contact with said poppet to open said port, said seventh chamber having an inlet connected to said P2 pressure, and a signal conduit connecting said sixth chamber to said means for venting said PC2 pressure.
 11. The ventilator of claim 6 having a manually adjustable pneumatically operated pressure relief valve connected to said patient airway conduit for venting pressure to atmosphere when it exceeds a preset value.
 12. The ventilator of claim 6 having a vacuum release valve connected to said patient airway conduit for admitting air to said airway conduit if the vacuum therein exceeds a predetermined value.
 13. The ventilator of claim 6 having a manually actuated sigh valve connected to said pressure PC2 and a sigh chamber to which gas at pressure PC2 is admitted when said manually actuated valve is opened, thereby increasing the capacity of the timing system and lengthening both the inspiratory and expiratory phases proportionately, with proportional increase in volume, while said manually actuated valve is held open.
 14. The ventilator of claim 6 having a control conduit connecting said exhalation valve to said patient airway conduit through a restriction and connecting exhalation valve to said exhalation valve control means and wherein said exhalation valve control means is connected to said pressure PC1 and comprises a diaphragm valve biased by a spring for venting said control conduit to atmosphere during said expiratory phase, said diaphragm valve being closed by said pressure PC1 overcoming said bias spring when said pressure PC1 is present during said inspiratory phase.
 15. The ventilator of claim 6 having pneumatically operated means for operating humidifying, nebulizing, and high-pressure exhalation means through an operating conduit, comprising pneumatic relay means connected to said pressure PC1 and to said pressure P3 for generating a pressure equal to PC1 and for conducting it to said operating conduit during said inspiratory phase and for bleeding said operating conduit to atmosphere during said expiratory phase.
 16. A fully pneumatic volume-cycled ventilator, providing inspiratory phases alternating with expiratory phases, including in combination: supply means for supplying a breathing gas at a first regulated pressure P1, regulator means connected to said supply means and having an outlet for said gas at a second, lower, pressure P2, pressure generating means connected to said regulator means for generating from said pressure P2 a first control pneumatic pressure PC1 upon the initiation of each inspiratory phase and holding said pressure at a constant value until the end of said inspiratory phase, Time control means connected to said pressure generating means for determining an inspiratory time for each breathing cycle, independently of the volume to be delivered, by generating a second pneumatic pressure PC2 from said pressure PC1, said second control presssure PC2 being always less than PC1 during the inspiratory phase and increasing during that phase from a minimum value to a maximum value, and for determining an expiratory time for the breathing cycle by bleeding said first control pressure PC1 to atmosphere upon the termination of each said inspiratory phase and decreasing said second control pressure PC2 during the expiratory phase from said maximum value to said minimum value, ratio control means connected to said time control means for determining the ratio of inspiratory time to expiratory time for each breathing cycle, flow control means connected to said supply means and to said pressures PC1 and PC2 for providing breathing gas at a rate dependent upon the difference between first and second control pneumatic pressures, PC1 and PC2, a patient airway conduit connected to said flow control means for conducting said breathing gas and having exhalation valve means, exhalation valve control means connected to said exhalation valve means and to said time control means for synchronizing said exhalation valve with said inspiratory and expiratory phases, and volume control means connected to said supply means, said time control means and to said flow control means at a pressure P3 for determining, independently of time, the volume of breathing gas delivered in each inspiratory phase by (1) varying the flow rate whenever the time is varied so that the volume delivered during the set time remains unchanged and by (2) enabling additional variation of the flow rate for any one time setting for changing the volume delivered while the time remains unchanged.
 17. The ventilator of claim 16 having a control conduit connecting said exhalation valve means to said patient airway conduit through a restriction and connecting said exhalation valve to said exhalation valve control means and wherein said exhalation valve control means comprises a diaphragm valve biased by a spring for venting said control conduit to atmosphere during said expiratory phase, said diaphragm valve being connected to said pressure PC1 and being closed by said pressure PC1 overcoming said bias spring when said pressure PC1 is present during said inspiratory phase.
 18. The ventilator of claim 16 having means for operating humidifying, nebulizing, and high-pressure exhalation means through an operating conduit, comprising relay means connected to said pressure PC1 and to said pressure P3 for generating a pressure equal to PC1 and for conducting it to said operating circuit during said inspiratory phase and for bleeding said operating conduit to atmosphere during said expiratory phase.
 19. A volume-cycled fully pneumatically operated pneumatic ventilator for connection to a supply of breathing gas, including in combination: pneumatically operated pressure generating means for generating from said supply a first control pneumatic pressure PC1 upon the initiation of each inspiratory phase and holding said pressure at a constant value until the end of said inspiratory phase, pneumatically operated time control means connected to said pressure generating means for determining an inspiratory time for each breathing cycle, independently of the volume to be delivered, by generating a second pneumatic pressure PC2 from said pressure PC1, said second control pressure PC2 being always less than PC1 during the inspiratory phase and increasing during that phase from a minimum value to a maximum value, and for determining an expiratory time for the breathing cycle by bleeding said first control pressure PC1 to atmosphere upon the termination of each said inspiratory phase and decreasing saiD second control pressure PC2 during the expiratory phase from said maximum value to said minimum value, pneumatically operated ratio control means connected to said time control means for determining the ratio of inspiratory time to expiratory time for each breathing cycle, pneumatically operated flow control means connected to said supply and to said pressures PC1 and PC2 for providing breathing gas at a rate dependent upon the difference between first and second control pneumatic pressures, PC1 and PC2, a patient airway conduit connected to said flow control means and including exhalation valve means, pneumatically operated control means connected to said exhalation valve means and to said time control means for synchronizing said exhalation valve means with said inspiratory and expiratory phases, and pneumatically operated volume control means connected to said supply, said time control means, and to said flow control means for determining, independently of time, the volume of breathing gas delivered in each inspiratory phase by (1) varying the flow rate whenever the time is varied so that the volume delivered during the set time remains unchanged and by (2) enabling additional variation of the flow rate for any one time setting for changing the volume delivered while the time remains unchanged.
 20. The ventilator of claim 19 wherein said time control means is connected to said pressure generating means for receiving said pressure PC1 by a parallel network of a check valve and a restriction, said check valve being opened during each inspiratory phase for rapid flow of gas at said PC1 pressure and closed during each expiratory phase, so that back flow to decrease said second control pressure PC2 is only through said restriction, which is sized to be effective at the shorter values of the time setting.
 21. A volume-cycled, completely pneumatically operated pneumatic ventilator for connection to a supply of breathing gas, including in combination: pneumatic time control means for determining the inspiratory time for each breathing cycle, independently of the volume of breathing gas to be delivered, by generating from said supply a first control pneumatic pressure PC1 upon the initiation of each inspiratory phase and by generating a second control pneumatic pressure PC2 from said pressure PC1, said first control pressure PC1 being present only during the inspiratory phase and constant during that time and dropping to atmospheric at the beginning of the expiratory phase, said second control pressure PC2 being always less than PC1 during the inspiratory phase and increasing during that phase from a minimum value above atmospheric to a maximum value, then decreasing during the expiratory phase from said maximum value to said minimum value, pneumatically operated ratio control means connected to said time control means for determining the ratio of inspiratory time to expiratory time for each breathing cycle, a patient airway conduit having exhalation valve means, pneumatically operated flow control means connected to said supply, said ratio control means, said time control means, said volume control means and said patient airway conduit, for providing breathing gas from said supply to said patient airway conduit at a rate dependent upon the difference between said first and second control pneumatic pressures PC1 and PC2, pneumatically operated control means connected to said exhalation valve means and to said time control means for synchronizing the operation of said exhalation valve means with said inspiratory and expiratory phases, and pneumatically operated volume control means connected to said supply and said time control means for determining, independently of time, the volume of breathing gas delivered in each inspiratory phase.
 22. The ventilator of claim 21 wherein said time control means is connected to said ratio control means for receiving said pressure PC1 by a parallel network of a check valve and a restriction, said check valve being opened during each inspiratory phase for rapid flow of gas at said PC1 pressure and closed during each expiratory phase, so that back flow from said pressure PC2 during the expiratory phase is only through said restriction, which is sized to be effective at the shorter values of the time setting, said ventilator also having means comprising part of said ratio control means for bleeding said pressure PC1 to atmosphere at the beginning of said expiratory phase.
 23. The ventilator of claim 21 having a manually actuated sigh valve connected to said time control means by a conduit into which said PC2 pressure is delivered, and a sigh chamber to which gas from said conduit is admitted when said manually actuated sigh valve is opened, thereby increasing the capacity of the timing system and lengthening both the inspiratory and expiratory phases proportionately, with proportional increase in the volume of breathing gas during said lengthened inspiratory phase, while said manually actuated valve is held open.
 24. A fully pneumatic volume-cycled pneumatic ventilator, providing inspiratory phases alternating with expiratory phases, including in combination: supply means for supplying a breathing gas at a first regulated pressure P1, regulator means connected to said supply means and having an outlet for said gas at a second, lower, pressure P2, a PC1 conduit, a PC2 conduit, a cycle generator having a housing with an inlet connected to the outlet from said regulator means and having a first diaphragm assembly with two diaphragms of different effective areas, with atmospheric pressure between them, a first seat at one end bounded by the smaller area diaphragm of said first diaphragm assembly, adapted to close said inlet or to open it to a first chamber, said first chamber having an outlet, a second chamber at the other end bounded by the larger area diaphragm of said first diaphragm assembly and having a port connected to said PC2 conduit, a compression spring in said second chamber urging said first diaphragm assembly to close said inlet, and an inspiratory-time-to-expiratory-time ratio determining screw assembly for regulating the compression of said spring, a fixed-orifice bleed connected to the outlet of said first chamber, said cycle generator also having a second diaphragm assembly with two diaphragms of different effective areas and a second seat, a third chamber at one end bounded by the larger area diaphragm of said second diaphragm assembly and having an inlet connected to the outlet from said first chamber and an outlet leading to said PC1 conduit via a spring-urged check valve which transmits the pressure of said first chamber to said PC1 conduit during each inspiratory phase and prevents back flow from said PC1 conduit into said third chamber at end of each expiratory phase, when said first seal closes said inlet to said cycle generator and while said third chamber bleeds to atmosphere through said fixed orifice bleed, a fourth chamber between the diaphragms of said second diaphragm assembly having a port connected to said PC2 conduit, and a fifth chamber at the other end bounded by the smaller area of diaphragm of said second diaphragm assembly having an inlet connected to said PC1 conduit, normally closed by said second seat and an outlet vented to atmosphere, for venting said PC1 conduit during each said expiratory phase, an inspiratory-time-determining valve, having an inlet connected to said PC1 conduit and an outlet connected to said PC2 conduit, for supplying said PC2 conduit with the gas at a varying pressure PC2 always lower than the pressure PC1 during each inspiratory phase, said time-determining valve having a logarithmically shaped stem and orifice and time-setting means for determining the position of said stem relative to said orifice and therefore the flow rate from said PC1 conduit to Said PC2 conduit, said PC2 pressure building up continuously during each said inspiratory phase to a maximum value set by said ratio-determining screw assembly, and continuously decreasing during said expiratory phase by bleeding through said PC1 conduit to atmosphere until it reaches a minimum value which is a set amount lower than said maximum value, the set amount being determined by the ratio of the effective areas of the two diaphragms of said first diaphragm assembly, an inspiratory volume-determining valve, having an inlet connected to said supply means, an outlet at a reduced pressure P3 and at a flow determined by the relative position of a plug within an orifice, the plug being shaped so that its position sets the area of passage according to a logarithmic function, first flow-setting means determining the position of said plug relative to its orifice entirely independently of said time-setting means and second flow-setting means also determining the position of said plug relative to its orifice in inverse ratio to the setting of said time, so that the volume delivered by said volume-determining valve remains the same when the time determining means alone is varied, a flow controller having a third diaphragm assembly of three diaphragms including two outer diaphragms of equal effective area and a central diaphragm of smaller effective area and having a third seat at one end, a sixth chamber at one end of said third diaphragm assembly having an outlet orifice toward and away from which said third seat moves, flow through said outlet orifice being varied according to the position of said third seat, said sixth chamber having an inlet connected to the outlet from said volume-determining valve at said pressure P3, said flow controller also having a seventh chamber adjacent to said sixth chamber, between said first outer diaphragm and the central diaphragm with a port connected to said PC2 conduit, an eighth chamber adjacent to said seventh chamber between the central diaphragm and the second outer diaphragm with a port connected to said PC1 conduit, and a ninth chamber at the opposite end of said diaphragm assembly from said sixth chamber with a port connected to said supply pressure P1, a compression spring in said ninth chamber bearing on said third diaphragm assembly, and means for setting the compression of said compression spring, whereby as said pressure PC2 increases during the inspiratory phase and said pressure PC1 remains constant, the outflow from said outlet orifice decreases from a maximum at the start of the inspiratory phase to a minimum at the end of the phase, and whereby the flow is shut-off during the expiratory phase as PC1 is at atmospheric pressure and PC2 is greater than PC1, a patient airway conduit connected to said outlet orifice of said flow controller, an exhalation valve in said patient airway conduit, and exhalation valve control means for said exhalation valve connected thereto and to said cycle generator for synchronizing the opening and closing of said exhalation valve with the initiation, respectively, of said expiratory and inspiratory phases.
 25. The ventilator of claim 24 having a control conduit connecting said exhalation valve to said patient airway conduit through a restriction and connecting said exhalation valve to said exhalation valve control means and wherein said exhalation valve control means is connected to said PC1 conduit and comprises a diaphragm valve biased by a spring for venting said control conduit to atmosphere during said expiratory phase, said diaphragm valve being closed by said pressure PC1 overcoming said bias spring when said pressure PC1 is present during said inspiratory phase.
 26. The ventilator of claim 24 having means for operating humidifying, nebulizing, and high-pressure exhalation means through an operating conduit, comprising relay means connected to said PC1 conduit and to the outlet of sAid inspiratory volume-determining valve at said pressure P3 for generating a pressure equal to PC1 and for conducting it to said operating conduit during said inspiratory phase and for bleeding said operating conduit to atmosphere during said expiratory phase.
 27. The ventilator of claim 24 wherein the inlet to said inspiratory-time-determining valve is connected to said PC1 conduit by a parallel network of a check valve and a restriction, said check valve being opened during each inspiratory phase for rapid flow of gas and closed during each expiratory phase, so that back flow is only through said restriction, the restriction being sized to be effective at the shorter expiratory times for which the ventilator can be set.
 28. The ventilator of claim 24 having an adjustable pressure relief valve connected to said airway conduit for venting pressure to atmosphere when it reaches a preset value.
 29. The ventilator of claim 24 having a vacuum release valve connected to said airway conduit for admitting air to said airway conduit if the vacuum therein exceeds a predetermined value.
 30. The ventilator of claim 24 having a manually actuated sigh valve connected to said PC2 conduit and a sigh chamber to which gas from said PC2 conduit is admitted when said manually actuated valve is opened, thereby increasing the capacity of the timing system and lengthening both the inspiratory and expiratory phases proportionately, with proportional increase in volume, while said manually actuated valve is held open.
 31. The ventilator of claim 24 having override means for actuation by a patient able to initiate a new inspiratory phase before completion of a controlled expiratory phase, comprising means connected to said patient airway conduit for sensing a patient-induced vacuum of given value, signal supply means for producing a pressure signal when said given value is sensed, and means for venting said PC2 pressure conduit from its then pressure to its minimum pressure upon application of said signal thereto.
 32. The ventilator of claim 31 wherein said means for sensing comprises a housing, a fourth diaphragm assembly in said housing having two diaphragms, one large area diaphragm and one small area diaphragm, with a tenth chamber between them connected to said airway conduit, the end with large area diaphragm of said fourth diaphragm assembly being vented to the atmosphere, the other end being open to an eleventh chamber and having a fourth seat, spring means in said tenth chamber, and sensitivity control means for setting the pressure exerted by said spring means against said diaphragm assembly, a detector assembly having a fifth diaphragm assembly open at one end to said eleventh chamber and having a tubular extension that provides an axial conduit and is opened and closed by said fourth seat, spring means acting on said fifth diaphragm assembly to urge it to open said axial conduit, twelfth chamber on the opposite end of said fifth diaphragm assembly, the motion of said fifth diaphragm assembly being limited to a fixed amount by internal configuration of said eleventh and twelfth chambers, a port venting said eleventh chamber to atmosphere, a passage through said fifth diaphragm assembly into said twelfth chamber from said axial conduit, an inlet connected to said P2 conduit and having a restricted orifice leading into said twelfth chamber, and a port connecting said twelfth chamber to said signal supply means.
 33. The ventilator of claim 32 having a relay for said detector assembly, comprising a sixth diaphragm assembly having a pair of diaphragms of equal effective area defining a thirteenth chamber on one side of said sixth diaphragm assembly, connected to the twelfth chamber for maintaining the same pressure as in said twelfth chamber, a fourteenth chamber between said diaphragms and vented to atmosphere, and a fifteenth chamber on the other side of said sixth diaphragm assembly, said sixth diaphragm assembly having an axial opening and a Passageway opening from said fifteenth chamber into said fourteenth chamber, a sixteenth chamber joined to said fifteenth chamber by a port, a poppet for opening and closing said port and having an extension for engaging said axial opening and closing it when engaged by said sixth diaphragm assembly, said sixth diaphragm assembly operating when in contact with said poppet to open said port, and an inlet into said sixteenth chamber connected to said P2 pressure, and a signal conduit connecting said fifteenth chamber to said means for venting PC2.
 34. A fully pneumatic pressure-cycled ventilator including in combination: supply means for supplying a breathing gas at a first regulated pressure , regulator means connected to said supply means and having an outlet for said gas at a second, lower, pressure P2, an airway pressure sensor and controller comprising a housing, a first diaphragm assembly in said housing having a large first diaphragm, a smaller diaphragm, a first chamber between them having a port, a second chamber on the other side of said large first diaphragm, vented to the atmosphere, a third chamber on the other side of said second diaphragm, a seat on said first diaphragm assembly in said third chamber, a first spring in said first chamber bearing against said first diaphragm assembly, and a second, lighter, spring bearing on said large diaphragm in said second chamber, sensitivity control means for varying the pressure of said first spring against said first diaphragm assembly, a second diaphragm assembly having a pair of diaphragms of different effective areas and open at one end to said second chamber, with a third spring in said second chamber urging said second diaphragm assembly away from said first diaphragm assembly, a fourth chamber between said pair of diaphragms having a port, the other end of said second diaphragm assembly being open to atmospheric pressure, said first and second diaphragm assemblies each having extensions causing said second diaphragm assembly to exert force on said first diaphragm assembly when pressure in said fourth chamber is sufficient to overcome the force of said third spring and the pressure in said first chamber, a detector assembly having a third diaphragm assembly open to said third chamber and carrying a tubular extension that provides an axial conduit having an end facing said seat and opened and closed by said seat, a fourth spring acting on said third diaphragm assembly to urge it to open said axial conduit away from said seat, a fifth chamber on the opposite side of said third diaphragm assembly from said third chamber, the motion of said third diaphragm assembly being limited to a fixed amount by internal configurations of said third and fifth chambers, a port venting said third chamber to atmosphere, a passage through said third diaphragm assembly into said fifth chamber from said axial conduit, an inlet connected to the outlet from said regulator means at pressure P2 and having a restricted orifice leading into said fifth chamber, and an outlet port from said fifth chamber, a control conduit having its pressure controlled by and identical to that of said outlet port of said fifth chamber, a second pressure regulator for setting the pressure applied to said fourth chamber, having an inlet connected to said control conduit and having an outlet, a conduit connected to said outlet of said second pressure regulator having a fixed bleed to atmosphere and connected to the port to said fourth chamber, a flow valve, having an inlet connected to said supply means at said pressure P1, a plug, an orifice, an outlet for gas at a reduced pressure P3 and at a flow determined by the relative position of said plug and said orifice, and flow-setting means determining the position of said plug relative to said orifice, a flow controller having a fourth diaphragm assembly having three diaphragms including two outer diaphragms of equal effective area and a centRal diaphragm of smaller effective area and having a second seat at one end, a sixth chamber at one end of said fourth diaphragm assembly having an outlet orifice toward and away from which said second seat is moved, flow through said outlet orifice being varied according to the position of said second seat, said sixth chamber having an inlet connected to the outlet from said flow valve at said pressure P3, said flow controller also having a seventh chamber adjacent to said sixth chamber, between said first outer diaphragm and the central diaphragm of said fourth assembly with a port connected to atmosphere, an eighth chamber adjacent to said seventh chamber between the central diaphragm and second outer diaphragm with a port connected to said control conduit, and a ninth chamber at the opposite end of said fourth diaphragm assembly from said sixth chamber, with a port connected to said supply pressure P1, a compression spring in said ninth chamber bearing on said fourth diaphragm assembly, and means for setting the compression of said compression spring, a patieairway conduit connected to said outlet orifice of aid flow controller and connected to the port of said first chamber, an exhalation valve in said patient airway conduit, and exhalation valve control means connected to said control conduit for opening said exhalation valve during each said expiratory phase and closing it during each said inspiratory phase.
 35. The ventilator of claim 34 having a second control conduit connecting said exhalation valve to said patient airway conduit through a restriction and connecting said exhalation valve to said exhalation valve control means, and wherein said exhalation valve control means comprises a diaphragm valve biased by a spring for venting said second control conduit to atmosphere during said expiratory phase, said diaphragm valve being closed by said control pressure overcoming said bias spring when said control pressure PC1 is above atmospheric during said inspiratory phase.
 36. The ventilator of claim 34 having means for operating humidifying, nebulizing, and high-pressure exhalation means through an operating conduit, comprising relay means connected to said control pressure and to said pressure P3 for generating a pressure equal to said control pressure and for conducting it to said operating conduit during said inspiratory phase and for bleeding said operating conduit to atmosphere during said expiratory phase.
 37. The ventilator of claim 34 having pneumatic means connected to said control pressure for determining a constant time interval, means for beginning said time interval at the beginning of each said expiratory phase, and means actuated upon completion of said time interval for initiating a new said inspiratory phase unless said inspiratory phase has already been started by patient effort during said time interval, said new inspiratory phase being subject to the stated conditions of the control pressure generating means.
 38. The ventilator of claim 34 having an adjustable pressure relief valve connected to said airway conduit for venting pressure to atmosphere when it reaches a preset value.
 39. The ventilator of claim 34 having a vacuum release valve connected to said airway conduit for admitting air to said airway conduit if the vacuum therein exceeds a predetermined value.
 40. The ventilator of claim 34 having a relay for said detector assembly, comprising a fifth diaphragm assembly having a pair of diaphragms of equal effective area defining a tenth chamber on one end, connected to said fifth chamber for maintaining the same pressure as in said fifth chamber, an eleventh chamber between said diaphragms and vented to atmosphere, and a twelfth chamber on the other end, said fifth diaphragm assembly having an axial opening in said twelfth chamber leading to a passageway opening into said eleventh chamber, and a patient airway chamber joined to said twelftH chamber by said port, a poppet for opening and closing said port and having an extension for engaging said axial opening and closing it when engaged by said fifth diaphragm assembly, said fifth diaphragm assembly operating when in contact with said poppet to open said port, and an inlet into said thirteenth chamber connected to said P2 pressure, and an outlet connecting said twelfth chamber to said control conduit.
 41. A ventilator operated solely by pneumatics and capable of both pressure-cycled and volume-cycled operation, including in combination: supply means for supplying a breathing gas at a first regulated pressure P1, pneumatically operated regulator means connected to said supply means and having an outlet for said gas at a second, lower, pressure P2, pneumatically operated pressure reduction and flow-rate determining means having an inlet connected to said supply means at the pressure P1 and having an outlet for gas at pressure P3, pneumatically actuated flow control means having an inlet connected to said flow-rate determining means and having an outlet and pneumatically controlled means for opening said outlet only when a first control pressure PC1 is above a second control pressure PC2 and for then supplying said outlet with breathing gas from its said inlet at a flow rate dependent on the instantaneous difference between said first and second control pressures, a patient airway conduit connecting said outlet of said flow control means to a patient to be ventilated, a master operations switch connected to said regulator means and having a first ''''volume-cycled'''' position and a second ''''pressure-cycled'''' position, first pneumatically operated pressure generating means connected to said master operations switch for generating from said pressure P2 the pressure PC1 at a constant value, for delivering said pressure PC1 to said flow control means as said first control pressure when said switch is in ''''volume-cycled'''' position, pneumatically operated time control means connected to said first pressure generating means for determining an inspiratory time for each breathing cycle, independently of the volume to be delivered, by generating the pressure PC2 from said pressure PC1 at a value lower than PC1 during said inspiratory phase and sending it to said flow control means as said second control pressure PC2 by causing said pressure PC1 to be present only during the inspiratory phase and to be constant during that phase, said pressure PC2 increasing continually during that phase from a minimum value to a maximum value, always less than said pressure PC1 during said inspiratory phase and for determining an expiratory time for a breathing cycle, by bleeding said first control pressure PC1 to atmosphere upon the termination of each said inspiratory phase and by decreasing continually said pressure PC2 during the expiratory phase from said maximum value to said minimum value, pneumatically operated ratio control means connected to said time control means for determining the ratio of inspiratory time to expiratory time for each breathing cycle, pneumatically operated volume-control means connected to said time control means and to said flow-rate determining means for determining, independently of time, the volume of breathing gas to be delivered in each inspiratory phase of said volume-cycled mode, second pneumatically operated pressure generating means connected to said regulator means and to said switch when said switch is in ''''pressure cycled'''' position, for generating a pressure PC3 when the pressure in said patient airway conduit drops below a first predetermined level, indicating an attempt by the patient to initiate an inspiratory phase of a breathing cycle, pnuematically operated means for ceasing generation of said pressure PC3 and for bleeding it to atmosphere when the pressure in said airway conduit attains a second predetermined level Well above said first predetermined level, said operations switch acting in said ''''pressure-cycled'''' position to connect said pressure PC3 to said flow control means as said first control means and for bleeding said pressure PC2 to atmospheric and for disconnecting said pressure PC1 from said flow control means, said operations switch acting in said ''''volume-cycled'''' position to disconnect said pressure PC3 from said flow control means.
 42. The ventilator of claim 41 having an exhalation valve in said patient airway conduit, and exhalation valve control means for opening said exhalation valve during each said expiratory phase and closing it during each said inspiratory phase.
 43. The ventilator of claim 42 having a control conduit connecting said exhalation valve to said patient airway conduit through a restriction and connecting said exhalation valve to said exhalation valve control means and wherein said exhalation valve control means is connected by said switch to said PC1 in the ''''volume-cycled'''' position and to said PC3 in the ''''pressure-cycled'''' position and comprises a diaphragm valve biased by a spring for venting said control conduit to atmosphere during said expiratory phase, said diaphragm valve (a) being closed, when said master operations switch is in ''''volume-cycled'''' position, by said pressure PC1 overcoming said bias spring when said pressure PC1 is present during said inspiratory phase and (b) being closed, when said master operations switch is in ''''pressure-cycled'''' position by said pressure PC3 overcoming said bias spring when PC3 is above atmospheric during said inspiratory phase.
 44. The ventilator of claim 41 having pneumatically operated means for operating humidifying, nebulizing, and high-pressure exhalation means through an operating conduit, comprising pneumatic relay means, connected by said switch, when in the ''''volume-cycled'''' position to said pressure PC1 and, when in the ''''pressure-cycled'''' position to said pressure PC3, said relay means in both modes being connected to said pressure P3, for generating a pressure equal to PC1 or PC3, according to the position of said switch, and for conducting it to said operating conduit during said inspiratory phase and for bleeding said operating conduit to atmosphere during said expiratory phase.
 45. The ventilator of claim 41 having pneumatic means connected to said pressure PC3 for determining a constant time interval, pneumatically operated means for beginning said time interval at the beginning of each said expiratory phase, and pneumatically operated means actuated upon completion of said time interval for initiating a new said inspiratory phase unless said inspiratory phase has already been started by patient effort during said time interval, said new inspiratory phase being subject to the stated conditions of the second pressure generating means.
 46. The ventilator of claim 41 having an adjustable pressure relief valve connected to said patient airway conduit for venting pressure to atmosphere, when it reaches a preset value.
 47. The ventilator of claim 41 having a vacuum release valve connected to said patient airway conduit for admitting air to said airway conduit if the vacuum therein exceeds a predetermined value.
 48. The ventilator of claim 41 having a manually actuated sigh valve connected to said PC2 conduit and a sigh chamber to which gas from said PC2 conduit is admitted when said manually actuated valve is opened, thereby increasing the capacity of the timing system and lengthening both the inspiratory and expiratory phases proportionately, with proportional increase in volume, while said manually actuated valve is held open in said ''''volume-cycled'''' mode.
 49. The ventilator of claim 41 having pneumatically operated override means for actuation in the ''''volume-cycled'''' mode by a patient able to initiate a nEw inspiratory phase before completion of a controlled expiratory phase, comprising a signal conduit for transmitting a pressure signal from said second pressure generating means at pressure PC3 when the pressure in said patient airway conduit drops below said first predetermined level and means connected to said signal conduit for venting said PC2 pressure conduit from its then pressure to its minimum pressure upon receipt of said signal.
 50. A fully pneumatically operated ventilator of the type free from electric circuits and supplying breathing gas to a patient via an airway conduit during an inspiratory phase and stopping the supply during an expiratory phase, characterized by incorporating two modes of operation, (a) a volume-cycled mode in which the ventilator supplies a predetermined volume of breathing gas to the airway conduit over a predetermined time during the inspiratory phase and then is actuated to the expiratory phase for a predetermined time, and (b) a pressure cycled mode in which the ventilator supplies the breathing gas to the airway conduit whenever the pressure in the airway conduit drops below a predetermined level and stops the supply whenever a predetermined higher pressure is attained in the airway conduit, said ventilator comprising gas inlet means shared by both said modes, gas regulator means connected to said inlet means and shared by both said modes, pneumatically operated flow control means shared by both said modes and separately connected to said inlet means and to said gas regulator means for controlling the rate of flow of gas to the patient, gas outlet means connected to said flow control means and shared by both said modes, a pneumatically operated exhalation valve shared by both said modes, in said airway conduit, pneumatically actuated pneumatic control switch means shared by both said modes and separately connected to said inlet means and to said regulator means and connected to said exhalation valve for operating said exhalation valve, pneumatically operated pressure sensing means shared by both said modes and connected to said outlet means and to said regulator and to said flow control means for changing said ventilator from an expiratory phase to an inspiratory phase when the patient makes an effort of a predetermined negative pressure sensed by said sensing means, and a two-position manually operated master operation switch for selecting which of said two modes is to be used at any one time, said master operation switch having a single handle for switching from one mode to the other by a single simple movement.
 51. The ventilator of claim 50 characterized by said pressure-cycled mode comprising a flow-rate-determiner and pressure-reducer means having an inlet connected to the supply of breathing gas, said flow control means having an inlet connected to said flow-rate-determiner and pressure-reducer means and having pneumatic control means for opening its outlet when the control pressure is above a predetermined minimum pressure and for closing it when the control pressure drops below the predetermined minimum pressure, said patient airway conduit connecting the outlet of the flow control means to the patient to be ventilated through said outlet means, and control pressure generator means connected directly to the supply, to the flow control means, and to the patient airway conduit, for generating the control pressure when the pressure in said airway conduit drops below a first predetermined level, indicating an attempt by the patient to initiate an inspiratory phase of a breathing cycle, and for ceasing generation of the control pressure and for bleeding said control pressure to atmosphere when the pressure in said airway conduit attains a second predetermined level well above the first predetermined level, thereby initiating the expiratory phase of the breathing cycle.
 52. The ventilator of claim 51 characterized in that said control pressure genErator means includes a first sensor for sensing the first predetermined level, a lock actuated by said first sensor for locking the control pressure generator means in generating position upon attainment of the first predetermined level, a second sensor for sensing the second predetermined pressure, and an unlocker actuated by the second sensor for unlocking said lock upon attainment of the second predetermined level.
 53. The ventilator of claim 51 characterized by a pneumatic timer connected to the control pressure for determining a constant time interval, a first initiator for beginning the constant time interval at the beginning of each expiratory phase, and a second initiator actuated upon completion of the time interval for initiating a new said inspiratory phase unless the inspiratory phase has already been started by patient effort during said time interval, the new inspiratory phase being subject to the stated conditions of the control pressure generator means. 